ISOCARDIIDA. 191 
Cypricardia is distinguished by the simple form of its hinge; it 
is based upon a cretaceous species, Cpr. carinata. 
GLOSSOCARDIA, Stolicz., 1870. Shell elongately trapezoid, sub- 
ventricose, concentrically striated, beaks tumescent, obtuse, close 
together as in Cypricardia; ligamental furrow narrow and long 
as in Isocardia; hinge with two cardinal and one posterior lateral 
tooth in each valve ; the supero-posterior cardinal teeth generally 
are more or less distinctly bifid, at least the one in the right 
valve, which has anteriorly a thin, subobsolete prolongation 
bent downward; it is separated from the inferior cardinal and 
bluntly tubercular tooth by a deep sickle-shaped groove, into 
which fits the similarly shaped antero-inferior cardinal tooth of 
the left valve; this tooth is provided on the upper side with two 
grooves, their distance being equal to the width of the pit into 
which the antero-inferior tooth of the right valve fits. C. obesa, 
Reeve (cxiv, 57). Mauritius. 
MICRODON, Conrad, 1842. (Cypricardella, Hall. Eodon, Hall, 
1877.) Shell ovate, subelliptical, or subquadrate ; concentrically 
striated; hinge of right valve with two cardinal teeth; the 
anterior tooth beneath the beaks; posterior tooth turned 
obliquely backwards, leaving a triangular pit, which is probably 
occupied by a tooth in the other valve. Anterior cardinal margin 
with a long narrow groove, apparently for the reception of a 
slender projection of the other valve; posterior side beveled 
from above, edge thin; ligament external, in a deep cavity ; 
-muscular scars distinct, shallow; pallial line simple. Fossil. 
Carboniferous ; Indiana. JZ. subelliptica, Hall. 
? G@ONIOPHORA, Phillips, 1848. Silur., Devon.; Eur.,N. Am. C. 
cymbeformis, Sowb. U. Silur.; England. 
CoRALLIOPHAGA, Blainv., 1824. 
Syn.—Lithophagella, Gray, 1847. 
Distr.—5 sp. Mediterranean, in the burrows of the Litho- 
domus ; sometimes two or three dead shells are found one within 
the other, besides the original owner of the cell. South Sea, 
Fossil; Hocene—. C. coralliophaga, Gmel. (cxiv, 58, 59). 
Shell long, cylindrical, thin, slightly gaping behind; hinge- 
teeth 2-2, and a laminar posterior tooth; pallial line with a wide 
and shallow sinus. 
ANisoponTA, Deshayes, 1860. 
Distr.—2 sp. I. Bourbon. A. complanatum, Dh. (exv, 64). 
Eocene ; Paris Basin. 
Shell transversely elongated, compressed, inequilateral ; hinge 
thick ; alarge conical tooth and a triangular socket in each valve ; 
ligament external. Anterior adductor scar very small, and 
comprised between two prominent ribs (one parallel and the 
