190 ISOCARDIIDA. 
inent incurved beaks, hinge with two cardinal and one thin or 
lamellar posterior lateral tooth in each valve ; ligamental groove 
long, narrow, marginal; right valve with a strong, grooved pos- 
terior and one oblique simple anterior cardinal tooth, the latter 
running from the beak more or less parallel to the lunular 
margin; left valve with a single posterior and a thick anterior 
cardinal tooth strongly prominent above. JI. Balinensis, Laube 
(exv, 58-60). 
CALLOCARDIA, A. Ad., 1864. Shell cordate and inflated like 
in Isocardia, posteriorly scarcely flexuous, thin and without 
epidermis; hinge of the left valve with two unequal cardinal 
teeth, the anterior angularly bent on itself in the middle with a 
triangular pit on either side and with four prominent cusps at 
the margin ; the posterior oblique, curved, narrow, but elongated, 
and with two indistinct marginal cusps; no lateral teeth are 
present; pallial line simple and muscular impressions semilunar. 
There isas yet only one (left! valve of this remarkable species, 
C. guttata, known from the Chinese Seas. The absence of the 
posterior lateral tooth, as well as the peculiar cuspidation of the 
two hinge-teeth, distinguish it. 
tsocuLIA, M’Coy, 1844. Under the name of JI. ventricosa, 
M’Coy (exv, 61) figures a very tumid, cordate shell with a few 
concentric distant constrictions, indicating stages of growth. 
The shell appears perfect and closed. 
Cypricarpta, Lamarck, 1819. 
Syn.—Trapezium, Muhlfeldt, 1811. Libitina, Schum., 1817. 
Distr.—13 sp. Red Sea, India and Australia; in crevices of 
rock and coral. Fossil, 60 sp. Jurassic—; North America 
and Europe. C. rostrata, Lam. (cxvi, 68, 69). 
Shell oblong, with an oblique posterior ridge; umbones 
anterior, depressed; ligament external, in deep and narrow 
grooves; cardinal teeth 2-2, laterals 1—1 in each valve, some- 
times obscure; muscular impressions oval (of two elements) ; 
pallial line simple. 
Animal (of C. solenoides) with mantle-lobes united, cirrated 
behind ; pedal opening moderate ; foot small, compressed, with a 
large byssal pore near the heel; siphons short, conical, unequal, 
cirrated externally ; orifices fringed ; palpi small; gills unequal, 
the outer narrower and shorter, deeply lamellated, united pos- 
teriorly, the inner prolonged between the palpi. 
APRICARDIA, Gueranger, 1867. Shell elongated, inequilateral ; 
hinge with one strong, recurved tooth in each valve, the tooth 
being in the left valve almost directly under the beak and in the 
right a little posterior to it ; to each tooth corresponds an equally 
large cavity in the other valve. This peculiar form resembling 
