BRITISH FOSSILS. 



Decade Y. Plate YI. Fig. A. 



PYRINA DESMOULINSII, VAR. PrATTII. 



[Genus PYRIN A. Desmoulins, 1835. (Sub-kingdom Radiata. Order Echinoder- 

 mata. Family Cassidulidae.) Body oval, tumid, flattened above and below ; ambulacra 

 simple, continuous, radient ; mouth central inferior, elliptical; anus posterior, supra- 

 marginal ; tubercles perforate ; genital pores four.] 



Diagnosis. F. testa tumidd, ambitii eUiptico postice leviter emarginato ; 

 vertice depresso ; basi suhconcavd ; mio in medio faciei posticcB excavato. 



References. Pyrina Desmouliusii, D'Archiac (1847), Mem. Soc. Geol. 

 France, 2nd ser. t. ii. pi. 2. p. 297., pi. 13. fig. 4. ; D'Orb. Prodr. 2., 

 p. 78. ; Agass. Cat., p. 92. Pyrina Prattii^ Forbes, Morris's Catal., 2nd edit. 

 (1854), p. 88. 



Several members of the family Cassidulidce have been already 

 presented in the Decades, more particularly of that division of it 

 which has simple, instead of petaloid ambulacra — Disaster, Galerifes, 

 Hyhoclypus. The species Laving this character (the Echinoneides 

 of Agassiz) are abundant in the cretaceous rocks ; two out of three 

 sections of the genus Galerites are quite characteristic of the Chalk 

 and Green Sand. 



Pyrina, which differs h'om Galerites chiefly in its oblong instead 

 of circular outline, is a genus of rather small, and generally very 

 convex urchins. It is difficult to distinguish from it those abnormal 

 specimens of Galerites upon which M. Desor founded the spurious 

 genus Glohator. Such specimens occur in the Upper Chalk of Kent, 

 and Upper Green Sand of Warminster, and differ from Pyrina 

 solely in their more circular forms. 



Description. — The original example of Pyrina Desmoulinsii, 

 figured and described by M. le Yicomte d'Archiac, in his " Rapport 

 sur les Fossiles du Tourtia,'' measures 22 mill, in length, 16 mill, 

 transversely, and llj in height. The specimen now figured 

 measures 24 mill, long, 19 wide, 12 high, and is therefore wider, 

 [v. vi.] 5 F 



