I2 4 



LAND AND FRESH WATER MOLLUSKS 



Old Fort Yukon, Alaska ! thirty miles below Tanana on the Yukon 

 River ! Lake Lindeman ; East Kootenai district, British Columbia. 



This form is very close to V. sibirica Middendorff , which however 

 has a more depressed apex and uniform fine sharp sculpture. V. 

 cristata is of the same type, but much smaller. 



Valvata mergella Westerlund. 



Valvata mergella WESTERLUND, Vega Exped. Vetens. lakt., iv, p. 209, pi. v, 

 figs. 22, a-d, 1885. 



Range. Port Clarence, near Bering Strait, Alaska (Vega) ; 

 Popof Island, Shumagins, in small ponds (Kincaid) ; Stewart River, 

 Yukon district (Canadian Geol. Survey). 



This is the largest species of its group, measuring 5 mm. high and 

 7 mm. wide, with four whorls. The aperture is markedly expanded, 

 the sculpture very fine and rather sharp. The protoconch in the Shu- 

 magin specimens is very minute. The expansion of the aperture tends 

 to narrow the umbilicus, as it were at the last moment. 



Valvata virens Tryon. 



Valvata virens TRYON, Proc. Acad. Nat. Sci. Phila., for 1863, p. 148, pi. i, 

 fig. n. BINNEY, Land and Fw. Sh. N. Am., in, p. 15, fig. 21, 1865. 



Range. Clear Lake, California, to Vancouver 

 Island, at Nanaimo. 



A well marked species of more than usually tro- 

 choid form, recalling V. piscinalis of Europe, but 

 large, more solid, and when in good condition of a pe- 

 culiarly elegant green tint. The figures given in 

 Tryon's description are of immature specimens. Bin- 

 ney figures an adult specimen but does not give 

 the measurements. 



Family VIVIPARIDJE. 



Genus Campeloma Rafinesque. 



FIG. 95. 



virens Try- 

 on, operculum, 

 magnified. 



FlG. 96. Campeloma decisum b, operculum. 



