340 CATOPYGUS. 



etage Senonien." Among the many varieties of Micrasters collected from the Chalk rocks 

 of the British Islands, I have seen no form that I can assign to Micraster brevis. I have 

 given a drawing of a good type form of this species for reference should any forms allied 

 to it be discovered in course of time; and have furnished numerous details for special 

 comparison. The wide ambulacra, with narrow elongated plates and wide-set pores in 

 the zones, the character of the tubercles in the plates (fig. 3 /and^), the structure of 

 the apical disc, with the uniform structural character of the five ambulacra, form an assem- 

 blage of points of structure which are very diagnostic of this species. My learned friend, 

 Monsieur Cotteau, considers this form to be a variety only of M. cor-testudinarbim ; in 

 reviewing the different varieties of this species he remarks,^ " in the south-west of France, 

 and in the basin of the Mediterranean, the variety which predominates is short and dilated 

 before, and wider than it is long. It is the M, brevis, Desor, which we can collect by 

 hundreds in the quarries of Villedieu and of Saint-Fraimbault, and in the Chalk of 

 Corbieres at Sougraigne and at Soulage (Aude)." 



Catopygus pyriformis, Golclftiss. PL LXXVIII, fig. 2 a, b, c. 



NucLEOLiTES PYRIFORMIS, Goldfuss. Petrcf. Germanise, p. 141, pi. 43, fig. 7, 1829. 

 Cattopygus — Agassis and Desor. Catal. raison. R. 6, An Sciences Nat., 



torn. 7, ser. 3, p. 158, 1847. 



— TENUiPORUs, — Ibid., ibid., K. 7. 



— PYRIFORMIS, d'OrUgny. Prodrome II, p. 271, Etage 22, 1850. 



Diagnosis. — Test ovate, posterior border produced and tapering, upper surface 

 depressed, posterior half most elevated and slightly carinated ; ambitus inflated, posterior 

 border narrow, truncated, vent in the middle covered by the beak-shaped termination of 

 carina, base flat, plastron elevated, oral aperture central, surrounded by five prominent 

 lobes with petaloidal expansions proceeding therefrom ; ambulacral areas narrow, equal 

 sized, poriferous zones with 10 — 12 pairs of pores set obliquely and well spaced out; 

 periprocte oblong, transverse, test thick, external surface covered with fine, close-set 

 granules lodged in depressed areolae excavated out of the test like the small concavities 

 around the top of a thimble, those on the base larger than those of the upper surface. 



Dimensions. — Antero-postcrior diameter yo of an inch ; transverse diameter across 

 the widest part of ambitus -^-^^ of an inch ; lieight ^o of an inch. 



Description. — I am indebted to Mr. E. T. Newton, F.G.S., Palaeontologist of the 

 Survey, lor calling my attention to this very beautiful Urchin, obtained by iMr. J. 

 P. Walker, P.G.S., of York, and said to have been collected from the Upper Greensand 

 of Warminster. This specimen was presented by hiin to the Museum of the Royal 

 School of Mines, Jermyn Street, where it is now contained. A careful examination of 

 1 ' Echinides du Depart, de la Sarthe," p. 323, 1861. 



