APPENDIX. 353 



YOL. III. 



PELECYPODA. 



Gyj^rinidse [p. 18*1]. 

 RouDAiRiA, Munier-Chalmas. 



Syn. — Trigonocardia, Zittel. 



Distr. — Cretaceous ; N. Africa, India. R. Drui, Mun.-Chal. 

 (cxv, 49-51). 



Shell trigonal or trapezoidal, thick, convex ; beaks prominent, 

 incurved, anterior, with a deep lunule under them ; posteriorly a 

 sharp keel, behind which the surface is smooth, the rest of the 

 shell being folded ; hinge-margin thick ; the right valve with 

 three cardinal teeth, the posterior one separated from the central 

 by a deep pit, and divided, the anterior tooth horizontal, there 

 is a strong posterior lateral tooth ; in the left valve the posterior 

 cardinal is small, the middle one very large, the anterior divided, 

 its branches diverging, posterior lateral tooth strong ; anterior 

 muscular impression upon a raised base ; ligament external. 



Ptychodesma [p. 269]. 

 Fourth line of description, for " Planorbis," read " Pec- 

 tunculus." 



