EXPLANATION OF PLATE XXL 



Fig. 1. PHYSA W,KROiMATlS. (Pilge 211.) 



a. Example from Utab. 



b. Another view of the Siiiiie. 

 Fig. 2. Phys.v BniDGEiiENSis. (Page 210.) 



a. An example rather less robust than the typical forms. 



Fig. 3. Hklix Leidyi. (Page 211.) 



«. A natural cast, the test beiug entirely removed. 



I). Another view of the same. 



i\ An example showing the surface-markiDg.s of the test. 



Fig. 4. Vivii'ARUS TuocmroRMis. (Page 214.) 



a. Typical form ; a medium-sized example. 

 h. Another example. 



c. Another, showing the apex quite comiilete. 



Fig. 5. ViviPARUS tkochlfokmis var. (Page 215.) 



a. Medium-sized example, showing aperture. 



h. Opposite view of the same. 

 Fig. 6. ViviPARus ionicus. (Page 215.) 



a. Upper view of rather small example. 



b. Side view of the same. 

 Fig. 7. ViviPARCS ? ?. (Page 215.) 



a. Side view of example of ordinary size, enlarged. 



b. Opposite view of the same. 

 Fig. H. Pi,anorws Utahen.sls. (Page 209.) 



n. Upper view of specimen, adult size. 

 Fig. 9. Gokiobasls Nebrascensis. (Page 213.) 



a. Example with revolving lines more than usually disiiuct. 



b. Another examijle, differentl}' and more faintly lined. 



c. Another, still differently lined. — All natural size. 

 Fig. 10. Goniobasis tenuicarinata. (Page 212.) 



a. Example with two carina!. Also showing nearly full form of aperture. 



b. xAnother with carinaj more than usually distinct and numerous. 



Fig. 11. Go.NioBAsis teneua. (Page 212.) 



a. A complete example, rather less than average size. 



b. Another similar example, opposite view. 



c. Another example, full average size. 

 Fig. 12. Unio vetu.stus. (Page 200.) 



a. Left valve. 



b. Interior, right valve. 



c. Interior, left valve. 



rf. Dorsal view of a partially-crushed example. 

 Fig. 13. Cyrena (Veloriiina) Durkeei. (Page 207.) 



a. Left valve, ordinary size. 



b. Hinge of right valve. 



