Genre   Protoscutella Stefanini, 1924, p.843

Relations between American and European tertiary echinoid faunas

Espèce type  Scutella mississippiensis Twitchell, 1915 (désignation originale)

Mesozoic and Cenozoic Echinodermata of the United States

Extension stratigraphique (bibliographique, non vérifiée) : Eocène inf (?) à supérieur

Protoscutella conradi (Cotteau,1891)

     Sismondia Conradi, Cotteau, 1891. Sismondia marginalis (non Des Moulins), Conrad, Catal. of the eocene amer. Echinod. U. S., Proced. Acad. Sc. Philadel., 2° sér., vol. IX, p. 75, 1869. Espèce subovale ou suborbiculaire, déprimée, élevée au milieu, arrondie sur les bords qui sont plus épais de l'aréa submarginale. Bord postérieur tronqué et émarginé. Périprocte subquadrangulaire, petit, rapproché du bord qui est renflé en dessous. Près Charleston (Caroline du Sud). Éocène. —Il ne nous a pas été possible de conserver à cette espèce le nom de marginalis qui, dès 1837, avait été donné par Des Moulins à un Sismondia tout différent.

Scutella (?) conradi (Cotteau).

Plate LXIV, figures 1a-d.

     Determinative characters. - Test small in size ; marginal outline subquadrate to suboval, the sides and posterior margin being truncated so that the posterior border is semiquadrate and the anterior border is semicircular ; the whole form much depressed, though centrally it rises in the form of a low gently rounded mound ; margin thin, with a small notch in the middle of the posterior edge ; under surface flat. Ambulacral petals elliptical, extending about halfway to the margin. Apex and apical system central, or slightly excentric anteriorly. Peristome small, subcircular ; ambulacral furrows simple and straight for over halfway to the margin, then becoming obscure. Periproct very small, subpentagonal or subcircular, inframarginal.

     Dimensions. - Length 21 millimeters, width 21 millimeters ; height 3 millimeters. This is Conrad's type, here figured for the first time.

     Description. - The species, though described by Conrad in 1865, has never been figured and is not very well known. There is some doubt in regard to its generic position. Gregory's remark that it should be transferred to the genus Monostychia is not agreed to, for the reason that the type reveals five genital pores and fails to show any continuation of the actinal grooves abactinally. The test is small in size, the type being about 11/36 inch in diameter and about 1/8 inch in height. In marginal outline it is subquadrate to suboval, with the sides and posterior margin truncated so that the posterior half of the border is semiquadrate and the anterior half semi-circular. The upper surface is so much depressed all around the marginal area as to be quite flat, or even slightly concave, but within the area covered by the ambulacral petals it rises in the form of a low, gently rounded mound with a rather broad, flattened summit. The margin is thin, though slightly thicker than the submarginal area, with a small notch in the middle of the posterior side. The under surface is flat. The apex is central or slightly excentric anteriorly, at the summit of the tumid central area.

     The interambulacral areas are relatively large. The whole surface of the test is covered with small uniform tubercles, which are slightly larger on the under side.

     The apical system is subcentral, at the summit of the central mound. The madreporite is relatively large, occupying the larger part of the area covered by the system, and faintly tumid. There are five genital pores near the edge of the madreporite and five small radial plates each perforated by a minute pore.

     The peristome is small, subcircular, central ; the ambulacral furrows simple, straight, and quite distinct for slightly more than half the distance to the margin, then becoming obscure. A small ridge extends from the peristome along the middle of each ambulacral furrow for a greater distance than the diameter of the peristome.

     The periprocte is very small, considerably smaller than the peristome, subpentagonal of sub-circular, situated on the under surface near the posterior margin, being about one-fifth the radius from the border.

     Related forms. - Of American forms S. (?) conradi most closely resembles S. tuomeyi and some of the smaller specimens of Periarchus lyelli, but is easily separated from these species by its subquadrate marginal outline and the inframarginal position of its periproct. It also resembles S. mississippiensis, but its periproct is less nearly marginal. It does not appear closely related to any of the known foreign forms.

     Locality. - Conrad said his type came from near Charleston, S. C.

     Geologic horizon. - Probably Cooper marl, upper Eocene.

     Collection. - Academy of Natural Sciences of Philadelphia (1081).

Planche LXIV (extrait) d'après Clark

Protoscutella conradi (Cotteau,1891) - Eocène inférieur, Castle Hayne Fm, Duplin Cty, Caroline du Nord, 23 mm

Protoscutella mississippiensis (Twitchell,1915)

Scutella mississippiensis Twitchell, n. sp.

Plate LIX, figures 1a-f, 2.

     Determinative characters.—Test variable in size; subcircular to subtriangular in marginal outline, broader than long, broadest posteriorly; the whole form greatly depressed, being thin and nearly flat around a narrow marginal area within which it rises very gradually and gently to the low, central apex; margin thin, with a small notch in the middle of the posterior edge; under surface flat. Ambulacral petals elliptical, extending about half way to the margin. Apical system central. Peristome small, circular; ambulacral furrows simple and straight for two-thirds or more of the way to.the margin, thon apparently forking symmetrically. Periproct very small, circular, almost at the ambitus though slightly inframarginal, at the edge of the notch in the middle of the posterior margin.

     Dimensions.—Specimen A: Length 50 millimeters; width 52.5 millimeters; height 6. millimeters. Specimen B: Length 52.5 millitheters; width 76 millimeters; height S millimeters.

     Description.—This new Scutella is one of the most abundant in the American Cenozoic deposits. The writer bas had opportunity to examine several hundred specimens. Neirly all of these were from the Eocene deposits of Mississippi, hence the specific name. The test is variable in size, ranging from less than inch to over 3 inches in diameter and from less than 1/8 to nearly 1/2 inch in height. The marginal outline is also quite variable, ranging from circular to subcircular in the younger forms to subtriangular and even transvcrsely elliptical in the larger forms. The whole form is much depressed, being thin and nearly flat around a narrow marginal area, although slightly more so posteriorly thon elsewhere, from wich it rises gradually and gently to the low, central apex. The margin is thin and faintly undulating, with a small notch in the middle of the posterior edge; the under surface is flat cxcept around the peristome, where it is slightly concave. The apex is central or subcentral, at the summit of the broad central tumid area.

     The ambulacral areas are narrow in the petaloid region but wide in the marginal region where they arc wider thon the interambulacral areas. The dorsal portions of the ambulacra are petaloid. The petals are subequal in length, the odd petal slightly longer and narrower thon the rest; elliptical in form, slightly open at the ends and extencl about half way to the margin. The poriferous zones are rather wide, about equal to the. interporiferous areas, though varying somewhat both among the petals on a single specimen or on different specimens, being slightly wider, equal to, or slightly narrower than the interporiferous areas; the limer row of porcs oval, outer row slitlike, pairs of pores conjugatcd. A few pairs of pores occur beyond the ends of the petals.

     The interambulacral arecs are large though somcwhat smiller both between the petals and et the margin than the ambulacral arecs. The whole surface of the test is covered with small uniform tubercles which are slightly larget. on the under side.

     The apical system is subcentral, at the summit of the central tumid area. The madreporite is relatively large, occupying the langer part of the arec covered by the system, and flush with the surface. There are five genital pores near the edge of the madreporite. One specimen studied possessed the abnormal feature of a double posterior genital pore. There are five small radial plates, each perforated by a minute pore.

     The peristome is very small, not over double the size. of the periproct, circuler, central or slightly excentric posteriorly; the ambulacral furrows simple and straight for two-thircls or more of the distance from peristome to margin, thon apparently forking symmetrically, each pair of branches continuing almost to the margin. The under side is revealed on few specimens, and on few can the furrows be made out.

     The periproct is very small, circuler, almost at the ambitus though slightly inframarginal, situated et the, under and inner edgc of the notch in the middle of the posterior margin.

     Related forms.—S. mississippiensis does not appear to be closely related to any other American form. It resembles Periarchus lyelli, in general appearance, and specimens have doubtless been erroneously labeled S. lyelli, in some collections; S. mississippiensis, however, is readily distinguished by its submarginal periproct, greater width, the notch in its posterior edge, and the fact that its tumid central area involves nearly the whole upper surface. It bears an interesting resemblance to the recent species Scutella parma, but differs from it in having less widely open petals, much narrower interporiferous arecs, a less circuler and more anteriorly pointed form, and in not having its periproct exactly marginal or et the ambitus.

     Of foreign forms S. patagonensis (Desor) Ortman, cspecially the "alate" form described by Ortman and fornierly known as Echinarachnius juliensis Desor from the Neocene of Patagonia, appears to be most closely related to S. mississippiensis. It is very siinilar in marginal outline, location of periproct, etc., but differs in having e less central apical system, longer petals, nar­rower interambulacral arecs, and in having its ambulacral furrows bcghming simply and thon forking in symmetrical curving branches almost immediately. S. subtetragona De Grateloup and S. striatula M. de Serres, both from the upper Eocene of France, aise present certain points of identity with S. mississippiensis. Each, however, differs from the American form in having four genital pores instead of five and in having the ambulacral furrows foré near the peristome.

     Localities.—Cemetery Branch (type), Radiate Banks, Spillman's Clam beel and other localities in and around Enterprise, Clarke County, Miss.; San Augustin, and 1 mile southwest of Palestine, Tex.

     Geologic horizon.—Claiborne group, middle Eocene. In Mississippi, et the base of the Lisbon mari. In Texas, hi the marine substage of the Claiborne.

     Collections.—U. S. National Museum. (137655, A; 137655a, B); Wagner Free Instituts of Science.

Planche LIX (extrait)

Suzanne McIntire

http://n2t.net/ark:/65665/m34c7f7ae4-4bed-405b-8271-871e8608da50

Suzanne McIntire

http://n2t.net/ark:/65665/m3ecf6efb5-17f2-4f82-bb89-0000a5950292

Protoscutella mississippiensis (Twitchell,1915) - Eocène, Caroline du Nord, U.S.A., 31 mm

Protoscutella mississippiensis (Twitchell,1915) - Eocène, Caroline du Nord, U.S.A., 34 mm

Protoscutella mississippiensis (Twitchell,1915) - Lutétien, Weches formation, Nacogdoches, Texas, U.S.A., 28 mm

Protoscutella mississippiensis (Twitchell,1915) - Lutétien, Winona Sand, Enterprise, Clarke Cty, Mississippi, USA, 35 mm

Genre   Periarchus Conrad,1866, p.21

Check list of the invertebrate fossils of North America

Espèce type  Sismondia alta Conrad,1865 (désignation originale)

Mesozoic and Cenozoic Echinodermata of the United States

Extension stratigraphique (bibliographique, non vérifiée) : Eocène inf (?) à supérieur

Subgenus Periarchus, Conrad. Description. - Rounded ; apex central ; ambuladra short, open at the ends wich are situated about half way between the apex and margin ; ambulacral space tumid ; margin and submargin thin ; anus nearer to the mouth than to the periphery. The typical species of Mortonia (Scutella quinquefaria, Say) is much thicker on the edge, and the anus is situated rather nearer to the periphery than to the mouth.

Periarchus lyelli (Conrad,1834)

Scutella.

     S. Lyelli. Suborbicular, much compressed on the margin, and very convex in the centre ; ambulacra five ; beneath flat, or slightly concave near the margin, with five radiating impressed lines, each of which near the middle has lateral branches ; one or two obscure intermediate lines. Diameter nearly three inches ; height half an inch.

     This fossil is very characteristic of the upper stratum of the Eocene, and occurs in vast abundance a few miles south of Claiborne, on the Alabama river ; at Claiborne it is rather rare ; it occurs, however, in every stratum of the Eocene, but a very few fragments only have been obtained in any but the upper portion of this formation.

     Determinative characters.—Test variable in size, subcirciilar to snbovate in marginal outline; much depressed, less so centrally where it rises in a gently rounded, convex mound of variable height; margin and wide submarginul area thin; under surface flat. Ambulacral petals subelliptical to suboblong, extending about half way to the margin. Apex and apical system central or subcentral, on the somewhat flattened summit of the tumid area. Peristome small, subcircular; ambulacral furrows simple and straight for about half way to the margin, then forking symmetrically. Periproct very small, subcircular, from one-third to slightly more than halfway from peristome to posterior border.

     Dimensions.—-Specimen A: Length 90 millimeters; width 90 millimeters; height 12 millimeters. Specimen B : Length 32 millimeters; width 31 millimeters; height 6 millimeters. Specimen C: Length 35 millimeters ; width 34 millimeters; height 5 millimeters.

     Description.—Considerable confusion exists in regard to this and allied forms in the various collections and in the literature. Conrad as early as 1834 gave an excellent description of the species but no figure. The same year Morton published a poor upper view only of a small form which he called Scufella hjelU Conrad, but gave no description. Conrad's form was a large specimen from Alabama, forms similar to which have easily been identified among the material studied by the writer. Morton's specimen was a small one, whose present whereabouts is unkno\vn, and was from a locality which is uncertain. Desor, Cotteau, and others, basing their action upon Morton's figure, have placed the species lyelli in the genus Sismondia. This is an error, as Conrad's form has all the characters of Periarchus. Unless his figured specimen is discovered, Morton's form must remain of doubtful character and is therefore placed among the doubtful and unrecognized species.

     Periarchus lyelli is one of the most abundant of the American Cenozoic forms, at times occurring in such numbers and with such constancy as to afford a valuable aid in determining the geologic horizon in which it is found. The test is variable in size, ranging from 1 to 31/2 inches in diameter. In marginal outline it is circular or subcircular to subovate, some specimens slightly others decidedly broader posteriorly than anteriorly. All around the area outside the ambulacral petals it is greatly depressed and quite flat; but within the petaloidal area it rises in the form of a gently rounded mound with more or less flattened summit, which ranges from 1/4 to 1/2 inch in height according to the size and age of the specimen. Sometimes the mound approaches a subcorneal form, but even then the sides are more or less convex. The margin of the test is thin and slightly undulating, both characters being most pronounced posteriorly; usually there are broad shallow notches opposite the ends of the posterior petals, though these may be inconspicuous or absent in the smaller specimens. The flattened marginal area, from the ends of the petals to the edge, is thin and wide, being about as wide as, or wider than the petals are long, and usually widest posteriorly. The under surface is flat or nearly so with a broad faintly depressed ring about midway between margin and peristome. The apex is central or slightly excentric anteriorly, at the summit of the tumid area.

     The ambulacral areas are narrow in the petaloid region but wide at the margm where they about equal the interambulacral areas. The dorsal portions are petaloid. The petals are of medium size; subecjual in length, the odd petal being slightly longer than the rest; subelliptical to elongate elliptical or suboblong in form; slightly open at the ends; extending half or slightly more or less than half the way to the margin. The poriferous zones are rather wide, almost as wide as the interporiferous areas; inner rows of pores nearly straight and parallel and formed of oval pores, outer rows of pores slitlike; pairs of pores conjugated. A few pairs of pores occur beyond the ends of the petals.

     The interambulacral areas are large, relatively wde between the petals (usually wider than the ambulacral areas), nearly uniform, and composed of large polygonal plates. The whole surface of the test is covered with small uniform tubercles which are slightly larger on the under side.

     The apical system is central or slightly excentric anteriorly, on the somewhat flattened summit of the central mound. The madreporite is relatively large, occupying the larger part of the area covered by the system and flush with the surface. There are five genital pores near the edge of the madreporite and five small radial plates each perforated by a small elliptical pore.

     The peristome is small, subcircular, central or slightly excentric anteriorly; the ambulacral furrows simple and straight for from one to two-thirds the distance to the margin, then forking symmetrically at an angle usually of about 45°, each pair of branches continuing almost to the margin. On well-preserved specimens, each branch may be seen to give off on the outside one important side branch at right angles about halfway between the fork and the margin, which side branches soon bend and in turn approach the margin. A small ridge extends out from the peristome for a short distance along each ambulacral furrow.

     The periproct is very small, about half the diameter of the peristome, circular or subcircular, situated on the under surface from one-third to slightly more than one-half the way from the peristome to the posterior border.

     Related forms.—This species presents so many variable features that several apparently distinct varieties of it might have been recognized and separately described—such as one with a transversely elongate subtriangular marginal outhiie, or one with pcrijiroct midway between margin and peristome—but in each case intermediate forms show a gradation between the possible variety and typical representatives of the species. P. lyelli Conrad is closely related to the American forms P. pileus-sinensis and P. protuberans, both of which, however, have a relatively higher and more conical central tumid area. P. protuberans is further distinguished by its characteristic swollen anterior interporiferous area and smaller petaloid area. P. lyelli also greatly resembles S. tuomeyi which, however, differs m being somewhat truncated posteriorly and in having its periproct nearer the posterior border. In superficial characters P. lyelli greatly resembles S. mississippiensis, but the latter is easily separated by the inframarginal position of its peripi'oct. It does not appear to be closely related to any of the foreign forms.

     Localities.—Near Claiborne (Conrad's type and our specunen A); Cedar Creek, Clarke County; St. Stephens, near Cocoa, Choctaw Coimty; and Clarksville, Ala.; Shubuta Creek, 21/2 miles north of Shubuta; Chickasawhay Eiver, near Shubuta; and Shell Prairie, near Pachuta, Miss.; 14 miles below Macon, Twiggs County, Ga.; Mount Enterprise, Rusk County, and 2 miles east of Alto, Clierokee County, Tex.; Castle Hayne (specimen B); City Rock Quarry, Smith Creek; and Rocky Pomt, near Wilmuigton, N. C.

     Geologic horizon.—Claiborne group (middle Eocene) and Jackson formation (upper Eocene). In Texas in the "marme substage" of the Claiborne. In Mississippi probably near the base of the Lisbon marl. In Alabama abundant in the Scutella zone at the base of the Jackson, "just above the Claiborne fossiliferous sand." In North Carolma, in the Castle Hayne limestone (upper Eocene or Oligocene).

     Collections.—Boston Society of Natural History (larger figured form) (1553, A); U. S. National Mxiseum (smaller figured fonu); Alabama Geological Survey; American Museum of Natural History ; Wagner Free Institute of Science ; Williams College ; Amherst College ; Johns Hopkins University (T 2003, B; T 2004, C).

Planches LXI et LXII (extrait)

Suzanne McIntire

http://n2t.net/ark:/65665/m362eb1eb9-832e-4e0b-b11c-122e50114708

Suzanne McIntire

http://n2t.net/ark:/65665/m39052aa7d-cfbb-4222-8325-9daa84a05324

Periarchus lyelli (Conrad,1834) - Eocène, Castle Hayne Formation, New Hannover Cty, Caroline du Nord, U.S.A., 29 mm