in T. WRIGHT (1857-1878) Monograph on the British Bossil Echinodermata of the Oolitic Formations
Vol.I - The Echinoidea, pages 346-350.
ECHINOBRISSUS SCUTATUS, Lamarck. Pl. XXXVI, fig. 2 a, b, c, d, e, f.
Test elliptical, sub-quadrate, rounded before, enlarged, expanded, and bilobed behind ; upper surface convex, more or less depressed ; sides tumid ; base concave ; apical disc small, excentral, nearer the anterior border ; dorsal valley wide, with perpendicular walls ; apex separated from the disc by an undepressed portion of test ; valley extending about two thirds the distance beween the vertex and border ; vent large and elliptical ; base concave, much depressed at the excentral mouth-opening ; peristome slightly pentagonal.
Dimensions.- Height, seven tenths of an inch ; antero-posterior diameter, one inch and three tenths ; transverse diameter, one inch and a quarter.
Description.- It is impossible to decide whether the urchin figured by Plot * in tab. ii, fig. 12, and by Lister ** (tab. 7, fig. 26), refers to this species or E. clunicularis, iu consequence of the omission of the anal valley in these figures, on which the true specific character strictly depends. Down to a very recent date, the two forms have been confounded with each other, although, when critically examined, the differences are very evident. The stratigraphical distribution of the two species is moreover well defined, E. clunicularis ranging from the superior zone of the Inferior Oolite to the Cornbrash, whilst E. scutatus is limited to the Calcareous Grit and other subdivisions of the Coral Rag. The abundance of this nucleolite in the Calcareous Grit near Oxford makes it highly probable that this was the form the older authors above cited had in view in their respective works. Lang's † "Echinites Cordatus quaternis radiis è duplici serie transversarum lineorarum conflatis" (tab. 35, fig. 1), probably represents a bad specimen of this urchin, in which the single ambulacrum had been obliterated. 'the specimen is described as being very rare, and was found in the hills around Baetstein and Luggeren. 1eske's ‡ figure of Spatangus depressus (tab. 51, fig. 1) apparently represents a quadrate depressed variety of this species, but in consequence of the anal valley beiug filled up with matrix, the true specifie character is concealed. Many authors are of opinion that the figure of Goldfuss § does not represent the true Lamarckian Scutatus, and Desmoulins has proposed to separate it, under the name Goldfussii, but after having studied a large number of individuals collected at Trouville, l have found many specimens with which the figure of Goldfuss entirely agrees. A sufficient mm'gin has not been allowed for the varieties which the same species exhibits when obtained from different localities. M. Agassiz's ║ figure of this nucleolite is very good, and represents, l think, the true type form of the species. This author participates in the opinion expressed by Desmoulins, in reference to which he says
"En revanche je pense avec M. Desmoulins que Goldfuss a identifié à tort l'espèce qu'il a décrite sous le nom de N. scutatus, avec le N. scutatus de Lamarck, dont nous nous occupons en ce moment. Ce dernier en effet n'affecte nullement cette dépression de la face supérieure postérieure qui est très saillante dans les figures de Goldfuss ; c'est au contraire à la face antérieure qui est la plus inclinée." "Afin de distinguer le N. scutatus, Lam., du N scutatus, Goldf. (qui n'a point encore éte trouvé en Suisse), M. Desmoulins a donné à ce dernier le nom de N. Golrlfussii." ¶
Professor Edward Forbes *** considered this species as a variety of N. clunicularis, and described it as "Var. a major, sub-depressa, la ta, lateribus, tumidiusculis. Spatangus depressus, Leske, ap. Klein, p. 238, t. 51, fig. 12 (copied in 'Enc. Meth.,' pl. 157, figs. 5,6). Nucleolites scutata, Lamarck, 'An. s. Vert.,' iii, p.35 ; Defrance, 'Dict. Sc. Nat.,' vol.xxxv, p.213. N. scutatus, Agassiz, 'Echin. Suiss.,' p.45, pl.7, figs. 19-21." This quotation shows my lamented friend's opinion when the description of his Pl. IX was written. At that time I believe he had not seen my Trouville specimens of E. scutatus, for on making with him a comparison of some type-forms of N. scutatus, Lamk., he readily admitted, after that examination, the specific differences existing between the N. clunicularis and the true Lamarckian species.
In my first memoir on the Cassidulidae of the Oolites, ¥ I grouped several individuals of this species with E. dimidiatus, Phil. At that time nearly all the English Coral Rag nucleolites were referred to Philips's species ; and I was only convinced of my error after I had examined a series of good type-specimens from Trouville, the original locality of Lamarck's species.
Echinobrissus scutatus, Lamk., when fully developed, is uniformly convex on the upper surface ; it is rather narrower before than behind ; its length nearly equals its breadth, when measured about the middle of the test ; the flanks are rounded and tumid (fig. 2c), and the posterior border is truncated (fig. 2b) ; the vertex is situated nearer the anterior than the posterior border, and in the centre thereof is placed the apical disc ; from this point the test slopes gently towards the posterior border, but more abrumtly to the anterior side (fig. 2c) ; the ambulacral areas are narrow, and nearly uniform in width, the posterior pair being a little broader than the anterior areas. The poriferous zones are petaloidal only on two thirds of the upper surface (fig. 2a,c). The pores of the inner row are round, those of the outer row form oblique slits ; on the flanks they are both round, more distant, and placed obliquely, thus ·.·. .·.· ; at the border they become very small, and at the base indistinct ; near the peristome they are again larger and more numerous ; in the more crowded portions of the zones there are from six to seven pairs of pores opposite one of the large plates, and where they are more distinct on the sides there are four small pairs opposite one plate.
The two anterior inter-ambulacral areas are narrower than the posterior pair (fig. 2 a). There are about sixteen plates in a column, each plate forming a double inclined plane, and having its surface crowded with small equal-sized tubercles, arranged close together in three or four rows (fig. 2 f) ; the postero-lateral pair are wider and longer, and contain more plates in each column ; in other respects they have a similar structure to the anterior areas. The single inter-ambulacrum is about as wide as the postero-lateral pair ; it is truncated behind, and its border is grooved by the anal valley ; this depression has a univorm width, is concave at its base and upper part, and there is always an undepressed portion of test between its termination and the apical disc (fig. 2a) ; the anal opening is round, and is seen at the end of the valley (fig. 2 a, d).
The apical disc is small and excentral ; it elements are so intimately soldered together, that the sutures in all my specimens are obliterated ; the madriporiform tubercle is large and occupies the centre of the disc ; it appears to cover the genital plates (fig. 2 e), and the four genital holes are large oblique slits, which extend into the inter-ambulacral areas (fig. 2 e).
The base is nearly flat at the sides, and slightly concave towards the mouth-opening (fig. 2 b). ln large, well-developed specimens, the inter-ambulacral are as are a little prominent, and the course of the ambulacra is marked by corresponding depressions in the test ; the poriferous zones are so feebly shown, that the pores can only be seen with a lens.
The mouth-opening is moderately large for a nucleolite ; it is situated in a depression opposite the apical disc, and is nearer the anterior than the posterior border (fig. 2 b) ; the peristome is pentagonal, and each angle of the pentagon corresponds to an ambulacral area ; the areas form inconsiderable petaloidal expansions as they radiate from the peristome, and the pores are crowded close together in the vicinity of the mouth-opening. The anal valley forms one of the distinctive characters of this species (fig. 2 a); it is of an ovate or lanceolate form, with a blunt apex ; in sorne specimens it appeal's as if a portion of the inter-ambulacrum had been dri1led out for the passage of the intestine ; in sorne individuals it extends only half tbe distance between the margin and the vertex, whilst in others it reaches two thirds the length ; in aIl the specimens I have examined, an undepressed portion of test separates the apical disc from the upper border of the anal valley ; inferiorly, the valley forms a considerable sulcus, grooves the centre of the area, dividing its posterior border, and producing the cordate or bilobed form this species assumes (fig. 2 a, b).
Affinities and diiferences.- I have already stated that E. scutatus was formerly considered by English naturalists to be a variety of E. clunicularis, Lhwyd, and as such its history is more or less connected with that species. Were a student, therefore, to endeavour to unravel its synonyms from the books alone, he certainly would be puzzled in his search, as the critical remarks on E. scutatus have more frequently been made on hook-statements than from an examination of specimens. If, however, a comparison be made between a series of E. clunicularis, Lhwyd, from the Cornbrash, with a corresponding series of E. scutatus, Lamk., from the Calcareous Grit, all doubts will be removed from the mind of the observer as to the specific differences existing between these species ; and in default of such specimens, a carefnl study of Mr. Bone's most excellent figures in our Plates XXIV and XXVI, with the ample magnified details he has given therein, will afford snfficient evidence for our conclusion.
E. scutatus, Lamk., so nearly resembles E. dimidiatus, Phil., that the latter has by many been considered to be a variety of the former ; this point, however, will be more properly discussed in the section devoted to the description of E. dimidiatus, Phil.
These are the only English nucleolites which at all resemble E. scutatus. Between aIl the other older species and this Corallian form the distinctions are numerons and selfevident. Between the newer Portland species, E. Brodeii, Wr., and E. scutatus, a detailed analysis will be given in the section on that species.
Locality and Stratigrpahical position.- I have collected E. scutatus, Lamk., from the Lower Calcareous Grit at Bullington-Green, near Oxford, where it was associated with Cidaris Smithii, Wright. I have discovered it was from this same quarry that the large type-specimen of the Cidarite figured in our Pl. II was obtained. I have gathered it from the Lower Calcareous Grit at Filey Brig, Gristhorpe Bay, and Scarborough Castle Hill, Yorkshire, and from the same formation at Marcham, and Faringdon, Berks. The Yorkshire specimens I chiseled out of blocks containing Pygurus pentagonalis, Phil., and other Calcareous Grit shells, and the Berkshire specimens were associated with Cidaris florigemma, Phil., and Hemipedina Marchamensis, Wright. I have collected it from the Coralline Oolite at Calne, Wilts, where it is very abundant in some beds. In one slab, about nine inches square, obtained from a large quarry near the town, there are about fifty specimens, more or less imperfect, closely laid together. Like other urchins, it appears to have been gregarious, and would be found in great numbers if its head zone was exposed. Cidaris florigemma, Phil., Hemicidaris intermedia, Flem., Acrosalenia decorata, Haime, Pseudo-diadema versipora, Phil., lie with it in the same slabs.
My friend, Charles Pierson, Esq., collected this species from a Pisolitic Oolitic rock - the Lower Calcareous Grit of English geologists - about one mile from Trouville, Calvados, where it is very abundant, and in a good state of preservation. M. Desor states that it is found in the Oxfordien of Trouville, and Vaches-Noires, Calvados, Lannois, Ardennes, and Chamsol, Doubs.
History.- The history of this species has been already so fully detailed in my analysis of its synonyms, that it is unnecesary to enter into any further details on the subject.
* 'History of Oxfordshire.'
¥ 'Annals and Magazine of Natural History,' 2d series, vol.ix, p.300.
** 'De Lapidibus Turbinates,' cap. ii, titulus xxvi.
† 'Historia Lapidum Figuratorum Helvetiœ,' tab. 35, p. 119.
‡'Additamenta ad Kleinii Echinodermata,' p. 238, tab. 51, fig~. 1, 2.
§ 'Petrefacta Germaniae' tab. 43, fig. 6.
║ 'Échinodermes Fossiles de la Suisse,' tab. vii, figs. 19-21.
¶ Ibid., partie première, p. 46.
*** 'Memoirs of the Geological Survey, decade 1, pl. ix.