LAMELLIBRANCHIATA. 123 



Anterior side rounded, posterior slightly truncated. 

 The lunule and lunette are shallow and ill-defined. 

 Measurements. Antero-posterior diameter, 12m.m. ; umbono- 

 pallial diameter, 11 mm.; thickness (across both valves), 8 mm. 

 Locality. Upware. 



CYPRINA SEDGWICKII, Walker, sp. 

 (Plate vi., fig. 12, a, b, c.) 



Sphcera Sedgwickii, Walker, An. and Mag. Nat. Hist., Novem- 

 ber, 1866, pi. XIIL, figs. 1, 2. 

 Cyprina angulata, var. Seeley, An. and Mag. of Nat. Hist., 



1867 (non Flem., non Sby.) 



Cyprina Sedgwickii, Keeping. List of Fossils in Bonney, 

 'Cambridgeshire Geology,' Appendix, p. 68. 

 Venus Catalog. Cret. Foss., Museum of Prac- 



tical Geology, 1878, p. 21. 



I append Mr Walker's description : 



" Shell globose, nearly equilateral, slightly gibbous, concentri- 

 cally furrowed, the stria; finer and more distinct towards the 

 ventral margin; ligament prominent; lunule large, distinct, 

 cordate." 



Measurements. Length, T6 in.; breadth, 1'5 in.; thickness, 

 1-3 in. 



The size is very constant ; besides the delicate growth striae, 

 the shell is usually zoned with gentle varices. There is a faint 

 posterior ridge running from the umbo to the postero-lateral 

 margin, in which the shell approaches the character of G. angulata. 



In outline and in thickness the species varies somewhat, the 

 length and breadth being in some specimens equal. Such forms 

 are also more tumid, and come to resemble C. regularis (D'Or- 

 bigny) of the gault. But the two species are distinct. 



Since Mr Walker described this shell as Sphcera Sedgwickii, the 

 hinge has been worked out in a number of specimens. There are 

 three cardinal teeth, the anterior one being under the lunule ; this 

 tooth is double in the right valve; there is a distinct posterior 

 lateral tooth. The pallial line is simple. Upon the inside cast 

 the adductor muscle-marks arc well seen, and the posterior ridge is 



