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, la. 



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. Plenroccra subulare Lea. M. 



40. Bythinella obtusa Lea. M. 



41. Anmicola Instrica Pils. B, C, H, in all cases feeding upon 

 weeds. 



42. Amnicola limosa Say. B, C, F, R, M, H. 



43. Ainnieola limosa Say var. porata Say. M. 



44. Amnicola cincmnaiiensix A nth. R. 



45. Vali-ata tricarinata Say. B, F, M, H, R, T, C. 



46. Valvata tricarinata Say var. bicarinata Lea. B, F, H, R, T, 

 C. 



47. Vnlrnta 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 cariuse 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 carinre. 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. Li/ogyrux browne! H. F. Carpenter. B, F, in muddy bot- 

 tom. 



49. Campeloma rufum Hald. F, M. 3 sinistral specimens of 

 this species were taken. 



50. Campeloma si<b*oli<1uni Anth. D. Adult specimens are 

 curiously depressed, closely resembling ]'iiijtm-a eubpurpwrea Say 

 with which it is found. 



51. rii'i/nirii .tiili/iiirjiiii-rti Say. D. 



