126 THE NAUTILUS. 
The stations searched have been fully described and located in 
the first part of this article. They will be hereafter referred to by 
letter as follows : 
Station B. Belle Lake. 
Station C. Clearwater Lake. 
Station D. Mississippi River at Bellevue, Ia. 
Station F. Clearwater River. 
Station H. Heath Lake. 
Station M. Mississippi River at Clearwater, Minn. 
Station R. Crow River, Rockford, Minn. 
Station S. A dry meadow at St. Michaels, Minn. 
Station T. Among damp moss in tamarack swamp at Clearwater, 
Minn. 
39. Pleurocera subulare Lea. M. 
40. Bythinella obtusa Lea. M. 
41. Amnicola lustrica Pils. B,C, H,in all cases feeding upon 
weeds. 
42. Amnicola limosa Say. B, C, F, R, M, H. 
43. Amnicola limosa Say var. porata Say. M. 
44. Amnicola cincinnatiensis Anth. R. 
45. Valvata tricarinata Say. B, F, M, H, R, T, C. 
46. Valvata tricarinata Say var. bicarinata Lea. B, F, H, R, T, 
47. Vulvata tricarinata Say var. simplex Gld. C. 
Notes.—Typical specimens occurred alone in the Mississippi River 
only. Of 132 specimens taken from there, none show any tendency 
toward the varieties. The carinz are very prominent ; specimens 
mostly large and dark colored. At all the other stations, specimens 
were much smaller, light in color and only in exceptional cases hav- 
ing three distinct carinze. In most cases the middle one is entirely 
wanting. The few specimens taken at Clearwater Lake are about 
equally divided among the three forms. 
48. Lyogyrus brownet H. F. Carpenter. 5B, F, in muddy bot- 
tom. 
49. Campeloma rufum Hald. F,M. 3 sinistral specimens of 
this species were taken. 
50. Campeloma subsolidum Anth. D. Adult specimens are 
curiously depressed, closely resembling Vivipara subpurpurea Say 
with which it is found. 
51. Vivipara subpurpurea Say. D. 
