VENERID^. 181 



Clementia, Graj^ 1840. 



Dist7\ — 6 sp. Australia, Philippmes. G. papyracea, Gray 

 (cxv, 43). 



Thin, oval, white ; ligament semi-internal ; posterior teeth bifid, 

 sinus deep and angular. 



Animal with long, united siphons, and a large erescentic foot, 

 similar to Dosinia. 



Thetis, Sowerby, 1826. 



Syn. — Thetironia, Stolicz., 18*70. 



Distr. — Cretaceous. T. major^ Sowb. (cxv, 44). T. hyalina^ 

 Sowb. (cxiv, .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 lai'ge, inclined forwards ; 

 margins thin, simple ; ligament narrow, inflated ; muscular 

 impressions submarginal ; pallial impression slight, with a pro- 

 found double sinuosity. 



J^ORA, Conrad, 1810. 



Distr. — ^. cretacea^ Conr. (cxxi, 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 ; nymphte 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 nearl}^ related to Isodoma, but 

 it appears to be very like C3'^clina and Thetis. The type species 

 in general external characters of the shell also closely resembles 

 some Cyprimerise. 



ScALDiA, Ryckholt, 1852. 



Dititr.~-2 sp. Carboniferous ; Belgium. S. Lambotheana^ 

 Ryck. (cxv. 45). 



Shell equivalve, roundly ovate, moderatel}^ tumid, with con- 

 centric striae 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. 



