30 



and its faces projecting beyond the planes of t]i(^ sliell ; 

 color chestnut; greatest breadth three-fourtlis of an 

 inch. Very abundant. 



Say gives tlie bn'adtli as half an inch. Tin; species 

 attains to nearly an inch in breadth in Chicago River, 

 and resembles P. macrostomus, White. I have forms 

 answering to Plan, corpulentus^ Say, and which I 

 believe to be irimUls ; and, also, the following which 

 are included in the synonomy of Plan, irlnoh/s ; 

 Plan, rer/f/larls, Lea,— an immature form ; Plan, 

 mcffastoma, DeKay ; Pla7i. irivoMs, var ; fallax, 

 Ilalde. It will be setni that the varieties are numerous. 

 T believe that the differences may be accountc^d for by 

 the character of the waters, chemical elements, station, 

 climate etc. 



1>V. A:\0ES »■*>» WICAKB.^AIII.S, Say. 



Shell has three whirls, carinated, color brownish ; 

 aperture large; color Avithin reddish, witli two white 

 lines corn^sponding witli the carina ; breadtli oiK^-half 

 inch. Abundant. 



SUBGENUS GYRAULUS, Agassiz. 



I>I.A:^'aKICIS nKFI.KCri S, Say. 



Shell dextral, depressed ; whirls five, minutely 

 wrinkled, texture thin, aperture large, color light horn ; 

 breadth five-sixteenths of an inch. Very abundant. 



l>f.A.^OIC1SI» I'AKVIJS, S.\Y. 



Shell horn color, whirls five, minutely wrinkled ; 

 concave above and beneath ; and equally showing the 

 volutions ; lip rounded ; breadth one-fifth of an inch. 



