56 SUPPLEMENT TO GREAT OOLITE MOLLUSCA. 



the lower portion of the anterior border is elliptically curved ; the base is nearly straight ; 

 the inner borders of the valves are crenulated ; the surface has closely arranged, delicate, 

 unequal, longitudinal striations, which are decussated upon the anterior side by others 

 which radiate from the umbones, and when the outer layer of the test has been removed 

 a series of strongly marked, radiating striations are exposed over the whole of the 

 valve ; both kinds of striations are also impressed more or less distinctly upon the 

 nucleus. 



This delicately ornamented Cypricardia might at the first glance be mistaken for a 

 depressed variety of Cypricardia cordiformis, Desh., a shell which in the young condition 

 possesses great differences of figure ; it will be found, however, that Cypricardia caudata is 

 more depressed, more trigonal, the anterior side more lengthened, and the posterior angle 

 much less defined, so that the portion of the surface posterior to it is even somewhat 

 convex ; but in Cypricardia cordiformis it is flattened or often slightly concave in some 

 instances ; the entire absence of ornamentation, both upon the test and the nucleus, is 

 another distinctive feature. The fine specimen figured has the area delicately preserved, 

 and exhibits the ligament ; the test is of moderate thickness, and the inner borders of 

 the valves are crenulated ; an exposed portion of the nucleus has striations corresponding 

 to those upon the inner layer of the test. 



Geological Position and Locality. The Cornbrash of Northamptonshire j also in the 

 Forest Marble of Wiltshire, obtained by W. Walton, Esq. 



ISOCARDIA MINIMA, Sow. Tab. XXXVI, figs. 1, 1 a. 



ISOCAEDIA MINIMA, Sow. Min. Con., t. 295, fig. 1. 



Phillips. Geol. York., i, t. 7, fig. 6. 



Morris. Catal., 1854, p. 204. 



? Quenstedt. Der Jura, p. 443, pi. 60, fig. 17. 

 Non ISOCARDIA MINIMA, Gold/. Pet., p. 211, t. 140, fig. 18. 



Testa crassa, lavigata, tumida, umbonibus parvis submcdianis incurvis, margine dorsali 

 oblique-curvato, lunula cxcavata ; lateribus striis concentricis crebris tequalibus, tenuissimis 

 instructis. 



Shell thick, smooth, convex ; umbones small, somewhat oblique, and placed a little 

 anterior to the middle of the valves ; dorsal border curved obliquely ; lunule excavated ; 

 the surface of the valves with very delicate, closely arranged, concentric striations. 



A smooth, short, rounded, and moderately convex shell, with rather small umbones, 

 quite different from the casts figured by Goldfuss and attributed by him to this species, 

 but which probably belong to the genus Cardium. 



The single figure given by Quenstedt is much more inflated, with larger umbones, 



