VENERID#. 181 
CLEMENTIA, Gray, 1840. 
Distr.—6 sp. Australia, Philippines. C. papyracea, Gray 
(exv, 43). 
Thin, oval, white ; ligament semi-internal ; posterior teeth bifid, 
sinus deep and angular. 
Animal with long, united siphons, and a large crescentic foot, 
similar to Dosinia. 
THETIS, Sowerby, 1826. 
Syn.—Thetironia, Stolicz., 1870. 
Distr.—Cretaceous. T. major, Sowb. (exv, 44). T. hyalina, 
Sowb. (exiv, 34). 
Shell thin, oval-subtrigonal, close, smooth, or concentrically 
striate; three unequal, parallel, narrow cardinal teeth in each 
valve, the posterior longest, lamelliform in the right, longer and 
thicker in the left valve; beaks rather large, inclined forwards ; 
margins thin, simple; ligament narrow, inflated; muscular 
impressions submarginal; pallial impression slight, with a pro- 
found double sinuosity. 
ora, Conrad, 1870. 
Distr.—4. cretacea, Conr. (exxi, 4). Haddonfield, N. J. 
Shell roundly ovate; right valve with three diverging cardinal 
teeth, posterior one bifid ; cardinal -plate broad, deeply channeled 
anteriorly, with a compressed, lateral tooth in the middle of the 
channel; plate deeply channeled posteriorly. Left valve with 
three diverging cardinal teeth, the anterior one A-shaped, 
oblique ; one distant anterior lateral tooth with a channel above, 
parallel with the cardinal margin; nymph crenulated on the 
upper margin, a distant narrow channel on the posterior hinge- 
plate; pallial sinus deep, reaching to a point in a line with the 
posterior extremity of the posterior cardinal tooth; rounded 
and somewhat ascending. 
Conrad says that this genus is nearly related to Isodoma, but 
it appears to be very like Cyclina and Thetis. The type species 
in general external characters of the shell also closely resembles 
some Cyprimerie. 
Soatpra, Ryckholt, 1852. 
Distr.—2 sp. Carboniferous; Belgium. §. Lambotheana, 
Ryck. (exy. 45). 
Shell equivalve, roundly ovate, moderately tumid, with con- 
centric strie of growth; muscular scars two, anterior larger 
than posterior ; pallial line with an angular, somewhat ascending 
sinus, as in Dosinia; hinge-line of the left valve with a single, 
tubercular, cardinal tooth below the umbo. 
