I^L^TE X^^I. 



Page. 

 Fig. 1. Sph^rium ? Idahoense 183 



1. A specimen consisting mainly of an internal cast, with some portions of the shell 



remaining. 



1 a. An outline to show the convexity of the same. 



Fig. 2. Sph^rium rugosum 182 



2. A rather small specimen, enlarged two diameters. 



2 a. A larger specimen, enlarged two diameters. 



■ 2 6. An outline to show convexity, enlarged two diameters. 



Fig. 3. Unio Haydeni 184 



3. View of left valve. 



3 a. Same view of a larger specimen. 



3 b. Internal cast, showing an impression of the hinge. 



Fig. 4. Unio belliplicatos 165 



4. Left, side of one of the larger specimens. 



4 a. Right view of a smaller individual of same. 



Fig. 5. Unio vetustus 16 



5. A young shell flattened hy pressure, with a part of the posterior broken away. 



(Original type of the species.) 



5 a. A large specimen, somewhat twisted over by oblique pressure, so as to hide the beaks. 

 5 6. A dorsal view of same. 



5 c. A smaller specimen of same. 



Fig. 6. Cyrena (Veloritina) Durkeei 167 



6. A medium-sized specimen. 



6 a. An anterior view of same, showing its unusually deep and well-defined lunule. 

 6 6. A larger individual. 



6 c. A very gibbous, short variety. 



6fl!. A dorsal view of same, showing the deep posterior dorsal concavity. 



6 e. A separate left valve, showing hinge. 



6/. A small, depressed variety, or possibly a distinct species. 



6g. An internal cast, showing muscular impression, and the slightly sinuous pallial lin©. 



