ISOCARDIID A. 189 
horizontally extending flexuous groove into which the infero- 
anterior cardinal tooth of the left valve fits, the supero-posterior 
cardinal of this valve is moderately prolonged, single or indis- 
tinetly bifid. 
ANISOCARDIA, Munier-Chalmas,1863. Surface radiately marked, 
umbonal ridge not angular. Cretaceous, Eocene. Type, V. 
elegans, Munier-Chalmas (cxv, 54-56), Kimmeridge clay, Havre. 
VENILICARDIA, Stol., 1870. Shell, of large size, strong and 
thick, the supero-posterior cardinal teeth are usually more or 
less bifid, the one in the right valve with a very easy curve at 
the anterior end, the antero-inferior cardinal teeth of both valves 
are long, flexuous, and their posterior ends are in both cases 
strongly thickened and tubercular. Jurassic, Cretaceous, Ter- 
tiary. Type, V. arcotica, Stolicz. Cretaceous; India. V. cordi- 
formis, d’Orb. (exv, 57). 
Famity ISOCARDIID A. 
Shell cordiform or transversely oblong, ventricose, sometimes 
carinated ; beaks sometimes subspiral; two cardinal and two 
lateral teeth in each valve,the anterior lateral tooth occasionally 
obscure or rudimentary ; muscular impressions narrow; pallial 
line simple. 
IsocarprA, Lamarck, 1799. 
Etym,—Isos, like, cardia, the heart. Heart-cockle. 
Syn.—Glossus and Glossoderma, Poli, 1791.  Bucardium, 
Muhlfeldt. Tychocardia, Romer. 
Distr.—5 sp. Britain, Mediterranean, China, Japan. Fossil, 
90 sp. Trias—; United States, Europe, South India. J. cor, 
Linn. (exiv, 53-55). 
Shell cordate, ventricose; umbones distant, subspiral ; liga- 
ment external; hinge-teeth 2°2; laterals 1—1 in each valve, the 
anterior sometimes obsolete. 
Animal with the mantle open in front; foot triangular, 
pointed, compressed ; siphonal orifices close together, fringed ; 
palpi long and narrow; gills very large, nearly equal. 
The heart-cockle burrows in sand, by means of its foot, leaving 
only the siphonal openings exposed._BuLWER. 
The Isocardia-shaped fossils of the old rocks belong to the 
genera Cardiomorpha and Isoarea; many of those in the 
Oolites to Ceromya. Casts of true Isocardia have only two 
transverse dental folds between the beaks, and no longitudinal 
furrows. 
MiocaRDIA, H. and A. Adams,1856. Shell without epidermis; 
beaks strongly curved, spiral; posterior umbonal slope cari- 
nated; surface concentrically ridged. J. Moltkiana, Chemn. 
(exiv, 56). 
OARDIODONTA, Stol., 1867, Shell cordiform, inflated, with prom- 
