PELECYPODA—PRIONODESMA CEA . 



401 



minute teeth, interrupted at beak by a triangular resilifer. Muscle 

 impressions two and small. Pallial sinus small. Differs from 

 Nucula in its more porcelainous structure, the presence of a pallial 

 sinus and in the usually entire margins of the valves ; also differs 

 usually in outline. Siluric-Recent. 



93. L. rostellata (Conrad). (Fig. 511, d.) Devonic. 

 Very small. Differs from L. diversa in its more elongate out- 

 line, more recurved posterior extremity, and finer striae. 



Hamilton : New York, Pennsylvania, Ontario. Portage : Penn- 

 sylvania. 



94. L. diversa Hall. (Fig. 511, c.) Devonic-Mississippic. 

 Very small. Length about twice the height. 



Hamilton and Portage of New York and Pennsylvania. Bed- 

 ford shale of Ohio. 



95. L. pandoriformis Stevens. (Fig. 511, a, b.) Mississippi. 



FlG. 511. a, b, Leda pandoriformis; c, L. diversa; d, L. rostellata, c and d 

 enlarged, X 2 - (J'al. N. Y., V. ) 



Large, with posterior extremity attenuate but subtruncate at its 

 end. 



Waverly : Ohio, Michigan. 



96. L. bellistriata Stevens. (Fig. 512, a, b.) 



Mississippi- Permic. 

 Large. Surface covered with fine and regular concentric striae. 



FlG. 512. a, b, Leda bellistriata (Ind. Surv. ); c, Leda parva, right valve 



(Md. Surv.). 



Widely distributed in the Carbonic from Ohio to Colorado. 

 Also in Mississippic of Tennessee (Waverly Group) and Michigan 

 (Marshall Group). Upper and Lower Permic of Kansas. 



