Length. 



Width 



23.50 



11.25 



24.50 



11.00 



25.00 



10.50 



22.75 



10.25 



21.50 



9.50 



20.50 



9.00 



19.50 



8.10 



ypes : Collection B 



296 THE CHICAGO ACADEMY OF SCIENCES. 



in, forming a distinct furrow and giving the columella the appearance 

 of a plait ; this is apparent in all of the specimens examined ; pillar 

 round and smooth, as in obrussa, nearly cylindrical, "the base of the 

 preceding whorl abruptly flattened around the insertion of the upper 

 end of the pillar.'"' 



Aperture length. Width. 



13.00 8.00 mill. Type 



13.50 7.50 - 



12.00 7.00 " 



13.00 5.10 " Cotype 



11.00 5.10 - 



9.75 4.50 " 



9.50 4.10 " " 



Collection Bryant Walker, thirteen specimens, Xo. 1L347 ; 

 cotypes, Academy of Natural Sciences, Philadelphia ; the Chicago 

 Academy of Sciences, three specimens, No. 23316. 



Type Locality: In small spring-brook flowing into Little Tra- 

 verse Bay, Petoskey, Michigan. 



Animal, Jaw, Radula and Genitalia: Unknown. 



Raxge : Michigan. Apparently an inhabitant of the Boreal (Ca- 

 nadian) life zone and of the Canadian region. 



RECORDS. 



Michigan: Brook, Petoskey, Emmet Co. (Walker). 



Geological Distribution : Unknown. 



Ecology : Inhabits a small spring-brook flowing into Little Tra- 

 verse Bay. 



Remarks : Pctoskcycnsis is the largest species of the obrussa 

 group of Lymna^as. It is at once known by its peculiar inner lip and 

 large umbilical chink, and by its large size and heavy spiral sculpture. 

 Mr. Walker says of it: "This species was at first supposed to be a 

 very thin, fragile form of the elongate variety of L. catascopium, char- 

 acteristic of the lake region. But upon cutting into the shell, the pe- 

 culiar shape of the axis forbode its reference to that species." (See 

 Nautilus, p. G.) 



Pctoskcycnsis is a very distinct species, not at all likely to be con- 

 founded with any other. It is very desirable that the anatomy should 

 be examined in order that its correct systematic position may be known. 

 It is provisionally placed in Simpsouia, but an anatomical examination 

 may place it in Stagnicola with catascopium or emarginata. 



Subgenus STAGNICOLA Leach, 1830. 

 1819. Stagnicola Leach, Proof-sheets, pp. 141. 145. 

 1819. Omphiscola Rafixesoue, Journ. de Phys., LXXXVIII, p. 423. 



