•76 



LAND AXD FRESH- WATER SHELLS OF N. A. [PART II. 



mantle is simple. As Adauson founded his genus on a species 

 having a simple mantle, his name is retained for the last section, 

 leaving Draparnaud's* later name for the first section. Thus any 

 confusion of synonymy is avoided. 



Pliysa lordi, Baikp. — Shell thin, quite large, corneous, tumid, 

 gibbous, aperture large ; outer lip acute, marked with an external white 

 or brownish line ; external surface very 

 Fig. 125. minutely decussated ; whirls six, the ^^S- 1-°- 



first two minute, tinged with black, the 

 last swollen, four times the size of the 

 others. Length from ^ to 1 inch, breadth 

 from J to 5. 



Lake Osoyoos, British Columbia. (Brit. 

 Mas.) 



This species is one of the largest of the pkijsa lordi. 

 genus, and is much swollen and gibbous. 

 The outer lip is generally marked with a streak of brown 

 edged with white, which mark is left in those specimens which are of 

 older growth, leaving a white callous-looking line of growth edged with 

 brown, nearly in the centre of the last whirl, which is very large — being 

 about four times the size of all the others put together. The two upper 

 whirls, which are very small, are of a black color. The surface of the 

 shell is finely decussately striated. 



The Physa heterostropha of Say abounds in the Sumas Prairie, on the 

 Fraser River ; but its place seems to be taken on the higher ground to- 

 wards the Rocky Mountains by the Ph. lordi {Baird.) 



Phijsa lordi, Baikd, Proc. Zool. Soc. London, 1863, p. 68. 



Physa lordi. 



Fig. 127. 



Physa lordi. 



I have given 'above the original description of 

 this species and Figs. 125 and 126, copied from 

 advance proofs of the plates illustrating the 

 British Boundary Commission Report. Fig. 

 12*7 is drawn from a specimen collected bj the 

 American Commission of the same Survey. 



This is the largest Xorth American species of 

 Physa yet described. 



' Draparnaud did not make this distinction in the genus, but his first 

 species has a fringed mantle. 



