LUCINID A. 913 
with two diverging cardinal teeth in each valve, the anterior 
being somewhat elongated and nearly horizontally extended. 
The absence of lateral teeth and the usual rounded and globose 
form readily distinguishes this group from Corbis. The group 
has been mistaken for Sphzra, under which name also most of 
the species appear to have been described. Triassic, Creta- 
ceous. C. Mellingt, Hauer (cxix, 54, 55). 
Unicarpium, d’Orbigny, 1852. 
Syn.—Mactromya, Agass. (part). 
Distr.—Jurassic and Cretaceous. U.impressum, Morris and 
Lycett (cxix, 58). 
Shell transversely oval, smooth or concentrically striate; 
hinge with a single cardinal tooth in each valve, and no lateral 
teeth. 
GoNnoDoN, Schafhaeutl, 1863. Shell ovate, tumid, apparently 
smooth ; hinge of the right valve with a very large median semi- 
circular broad tooth with the sharpened edge turned upwards, 
that of the left valve with an equally large corresponding pit 
below bounded by a long thick tooth somewhat smaller than 
that of the other valve; the posterior margins of the hinge are 
thickened in both valves. This group differs from Unicardium 
by the enormous development (natural?) of the teeth. Type, 
U. ovatum, Goldfuss.  Lias. 
ConcHOCELE, Gabb, 1866. 
Type, C. disjuncta, Gabb. Tertiary ; California. 
Shell subquadrate, posteriorly less high and elongated, being 
very inequilateral, a ridge passing from the beaks to the pos- 
terior end; hinge edentulous, hinge-area somewhat thickened and 
insinuated under the beak with a single long rib-like tooth 
extending from the beak to the posterior end. As to internal 
characters this genus hardly appears to differ from some forms 
of Unicardium in which the cardinal tooth is obsolete, but the 
shape of the shell is different. 
FImprRiELLA, Stoliczka, 1870. 
Type, &. levigata, Sowb. (exix, 59). Cretaceous; England. 
Shell suborbicular, moderately tumid, subequilateral, with 
prominent, obtuse, incurved beaks, surface partially smooth, 
partially finely punctate or spinulous; lunular edge in front of the 
beaks somewhat expanded, hinge in each valve with two conical 
or subtubercular cardinal teeth: those of the right are superim- 
posed, the upper one being situated on the enlarged lunular 
margin, those of the left valve are situated beside each other, 
the anterior much stronger than the posterior, no lateral teeth 
are present, but the margin is posteriorly internally slightly 
