196 VERTICORDIID^. 



valves. Fossil. Eocene ; France. L. aviculare, Lam. (cxvii, 1). 

 These shells present considerable resemblance to Tridacna. 



GOLDFUSSiA, Castclnau, 1843, is based upon Cardium nautiloides, 

 each valve of which is said to resemble a laterally compressed 

 nautilus, keeled on either side. Silurian ; South America. 



? Dexiobia, Winchell, 1863. 



DUtr. — Devon., Carb. ; TJ. S. 7). ouaf a, Hall. 



Shell thin, inequi valve, inequilateral ; beaks separated by an 

 undefined area ; right valve very ventricose, with a very promi- 

 nent umbo, and a produced, incurved beak strongly inclined 

 forward; left valve much less inflated, with a less prominent 

 beak, scarcely elevated above the dorsal margin ; hinge-line 

 more or less extended, straight or slightly bent, edentulous ? 

 furnished with a thickened cartilage-plate bearing a lineal pos- 

 terior groove ; pallial line and muscular markings unknown. 



Cardiopsis, Meek and Worthen, 1861. 



Diatr. — Several palaeozoic species ; U. S. C. raditita, M. and W. 

 (cxvi, 95). 



Shell equivalve, somewhat inequilateral, very slightly oblique, 

 ovate or cordiform, entirely closed ; beaks rather elevated, 

 distinctly incurved, and directed towards the anterior side ; 

 surface marked by radiating striae or costse ; cardinal margin 

 short, and rounding into th^ posterior border ; hinge provided 

 with one or two distinct anterior teeth in each valve, near the 

 beaks (ligament and muscular impressions unknown). 



Byssocardium, Munier-Chalmas, 1882. 



Distr. — 2 sp. Eocene and Miocene ; France. B. emargin- 

 atum^ Desh. 



Shell allied to Lithocardium, but characterized by an anterior 

 opening for a large byssus, having margins toothed like those of 

 a Tridacna ; anterior muscular impression very feeble, placed 

 below the posterior cardinal tooth. 



Family YERTICORDIIDJE. 



Shell equivalve, or nearly so, of small size, inflated, with the 

 beaks incurved, closed all round, more or less solid, pearly 

 inside ; hinge with few cardinal teeth, more or less obsolete, 

 ligament subinternal or internal ; two muscular impressions, 

 pallial line simple. 



The animal of V. Japonica has the mantle-margins united, 

 with a small anterior opening for the protrusion of the foot, 

 which is small, triangular, compressed, and a posterior roundish, 

 fringed opening in which are inclosed two separated but very 

 short siphons ; labial palps small. 



