302 J. Walter Gregory — On Rhynchopygus Woodii. 



Mouth anterior : situated in the deeper part of the depression. 

 Eloscelle well marked. 



Periproct wide and forming a deep concavity in the posterior 

 margin : it is protected above by the prominent supra-anal rostrum. 



Tubercles small in impressed areolae : generally uniform, but 

 largest along the actinal ai - ea. 



Dimensions — Calculated from Prof. Forbes' type (fig. 5). 



Length 48 mm. 



Width: at apical disc 34 ,, 



„ maximum ... ... ... 40 ,, 



Height 15 ,, 



Distribution — Coralline Crag, Layston Eoad Pit, Aldborough [Brit. 

 Mus. E. 3207]. Red Crag: Bullock Yard Pit? 1 The locality of 

 the type specimens is doubtful. Forbes mentions none, but Morris 2 

 attributes the species to Suffolk. The condition of the specimens 

 and matrix suggests Walton-on-the-Naze. 



Affinities of the Species — The genus Rhynchopygus dates from the 

 Cretaceous ; from the species of this system and from the Eocene, 

 viz. B. marmini (Desmoul.) 3 of the Maestrichtien; B. pygmceus, Dune, 

 and Slad., i and B. calderi (d'Arch. and H. 5 ), from the Eanikot and 

 Khirthar series ; B. navillei, Lor., 6 B. thebensis, Lor., and B. zitteli, 

 Lor., 7 from the Egyptian Eocene, — B. Woodi may be readily distin- 

 guished by the greater development of the supra-anal rostrum. In 

 this species it extends back as far as the end of the test, whereas in 

 the above forms it occurs but as a more or less slight prominence, 

 on the posterior slope. B. siutensis, Lor., 7 also from Egypt, differs 

 in its thicker margins and less conical abactinal surface. The 

 remaining species of the genus, as at present limited, are two 

 existing American forms, and with these B. Woodi is more nearly 

 allied; B, pacificus (A. Ag.) 8 has a more central apical disc and a 

 different general shape, the posterior side being more sloping and 

 there is no lateral tapering towards the anterior. B. caribbcearum 

 (Lam.), 9 found also in the Pleistocene of Guadeloupe is the closest 

 ally of B. Woodi, and here again the greater prominence of the 

 supra-anal rostrum in the latter forms a ready means of distin- 

 guishing them. 



The affinity of Bhynchopygus Woodi to the two species last 



1 A. and E. Bell, " On the English Crags," Proc. Geol. Assoc. London, vol. ii. 

 1872, p. 197. 



2 Morris, Cat. Brit. Foss. 2nd ed. 1854, p. 78. 



3 Desmoulins, Etudes sur les Echinides, 1837, p. 360. 



4 Duncan and Sladen, The Fossil Echinoidea of W. Scinde, Pal. Indica. ser. xiv. 

 vol. i. (3) fasc. ii. 1882, pp. 68-9, pi. xv. figs. 5, 6. 



5 D'Archiac and Haime, Description des animaux fossiles du groupe numniulitique 

 de l'Inde, t. i. p. 352, pi. xxx. fig. 19. Paris, 1853. 



6 De Loriol, Monographie des Echinides contenus dans les couches nummulitiques 

 de l'Egypte, Mem. Soc. phys. et d'hist. nat. Geneve, vol. xxvii. i. p. 85-8, pi. iv. 

 figs. 2-4. 



7 De Loriol, Eocaene Echinoideen aus Aegypten und der libyschen Wiiste, 

 Palseontographica, vol. xxx. (3) pp. 18, 19, pi. ii. figs. 9-12. 



8 Al. Agassiz, " List of the Echinoderms sent to different Institutions with 

 Annotations," Bull. Mus. Comp. Zool. vol. i. No. 2, p. 27, 1863. 



9 Lamarck, Hist. nat. anim. S. Vert, p. 349, 1801. 



