OP THE PUKBECK FORMATION. 343 



This is one of the suboblong forms of the genus, slightly broader 

 (higher) in front than behind, and more boldly and obliquely curved 

 anteriorly than posteriorly ; the dorsal and ventral margins nearly 

 parallel ; the notch often strong, but sometimes obscured by 

 tubercles ; the contact-margins are much like those of C. granidosa 

 (fig. 21) ; the beak sometimes almost obsolete, but traceable. The 

 surface is punctate, with coarse, subcircular, close-set pits, giving 

 an appearance like that of a thimble-top ; it also bears numerous, 

 large, scattered tubercles, somewhat variable in their strength and 

 position; occasionally long, thick, and blunt, as noticed in E. 

 Forbes's letter to Mr. Bristow, see above, p. 314, where he terms 

 it " C. spinosa." Specimen Xb^, Mus. Pract. GeoL, shows an in- 

 dividual of this kind, with long thick tubercles ; it is strongly 

 beaked, much more so than our fig. 22, PI. YIII. In fact this 

 specimen is rather longer than the typical form, and is less strongly 

 beaked ; and it ought to be regarded as a variety, adjuncta. 



Edge-view long-ovate ; end-view short-ovate (figs. 23 and 24). 



The coarse tubercles remind us of a similar feature in Cytheridea 

 torosa (Jones); but in the latter they are fewer and relatively 

 larger, and the hingement of the valves is different. 



C. tuhercidata is not common. It comes from the Mid-Purbeck 

 of Durlston Bay (Xb^-, M. P. G.) ; and from the Upper Purbeck of 

 Mewps Bay (specimen no. 27, fig. 22, PL YIII.), and of Bacon Hole 

 (specimen in the British Museum, and Xb|-, M. P. G.). This last is 

 like the Wealden specimens figured in Eitton's Memoir, which are 

 strictly Weaiden, but do not occur nearly so frequently as Cyihere 

 Fittoni (Mantell), which was figured with them in fig. 2, pi. 21, of 

 Eitton's Memoir, and has been often mistaken for C. tuberculata. 



The Purbeck form (var. adjuncta) occurs also, I believe, in the 

 Weaiden beds, Eccleston Glen, Hastings. The Weaiden species I 

 hope to treat in full at a future opportunity. 



Eomer, 1839, evidently had C. tuhercidata, Sow., in the black 

 Cypridiferous Shales of North Germany, and Dunker, in 1846, 

 repeats the observation ; but his figure is very doubtful. 



II. Genus Ctpeioke, gen. nov. 



Animal unknown. Carapace bivalved ; subcylindrical ; right 

 valve rather larger than the other ; contact-margins ridged and 

 furrowed almost continuously, but the flanges and corresponding 

 ledges run closer together in some specimens than in others. Hinge- 

 line along the slightly convex back-edge not specially defined. 

 Valves smooth, elongate-oblong, with rounded ends, in the only 

 species yet recognized. 



The structure of the contact-margins of these valves is not 

 essentially different from that in Cypridea, except that the latter 

 has its characteristic antero-ventral notch. Qypridea, moreover, 

 has much coarser and thicker valves, and always differs in shape. 



The outlines of the carapace under notice approach those of Bar- 

 winula ; but in the latter the valves meet with simple edges and 

 considerable overlap ; and, as no other genus among the Ostracoda 



2b2 



