APPENDIX. 517 



greater in proportion to its breadth than in the other American 

 species, by the subrhoniboidal form of the posterior half, and 

 generally, by the color of the nacre, though this is not to be 

 relied on. It appears to belong to the genus Symphynota of 

 Mr. Lea. 



ALASMODONTA. 



13. Alasmodonta complanata, Barnes. Symphynota com- 

 PLANATA, Lea. Shell Lake, River St. Croix, Upper Mississippi. 

 Many species of shells found in this lake grow to an extraordinary 

 size. Some of the present collected by Mr. Schoolcraft, measure 

 nineteen inches in circumference. 



1-1. Alasmodonta hugosa, Barnes. St. Croix River, and Lake 

 Yaseux, St. Mary's River. 



15. Alasmodonta marginata, Say. Lake Vaseux, St. Mary's 

 River; very large. 



16. Alasmodonta edentula? Say. Anodon aeeolatus? 

 Sicainson. Lake Yaseux. The specimens of this shell are too 

 old and imperfect to be safely determined. 



UNIO. 



17. Unio tuberculatus, Barnes. Painted Rock, Upper Mis- 

 sissippi. 



18. Unio pustulosus. Lea. Upper Mississippi, Prairie du 

 Chien, to Lake Pepin. 



19. Unio verrucosus, Barnes, Lea. St. Croix River of the 

 Upper Mississippi. 



20. Unio plicatus, Le Sueur, Say. Prairie du Chien, and 

 River St. Croix. 



The specimens of U. plicatus sent from this locality by Mr. 

 Schoolcraft have the nacre beautifully tinged with violet, near 

 the posterior border of the shell, and are also much more ventri- 

 cose than those found in more eastern localities, as Pittsburg, for 

 example ; at the same time, I believe them to be of the same 

 species. Similar variations are observed in other species; the 

 specimens from the south and west generally exhibiting a greater 

 development. 



21. Unio trigonus. Lea. From the same locality as the last, 

 and like it unusually ventricose. 



