THE NAUTILUS. 141 



A NEW SUBSPECIES OF POLYGYRA MULTILINEATA SAY. 



BY WM. A. NASON. 



Polygyra multilineala algonquinensis n. subsp. 



The shell is smaller than multilineata, color varying from white 

 translucent to dark horn or chestnut, banded with reddish brown or 

 unicolorous, rather thin and fragile, peristome moderately reflected, 

 white. 



Greater diameter 17 mm., 32 specimens. 



Greater diameter 17.5 mm., 24 specimens. 



Greater diameter 18 mm., 72 specimens. 



Greater diameter 18.5 mm., 41 specimens. 



Greater diameter 19 mm., 54 specimens. 



Algonquin, McHenry Co., Illinois. 



Cotypes in collections of Bryant Walker, Acad. Nat. Sci. Phila., 

 Chicago Academy of Sciences, and Arthur F. Gray. 



All the specimens collected were examined, 284 in number, and 

 their average size is expressed in the above table of measurements. 

 The largest specimens found were three which measured 21 mm. in 

 greater diameter, and the two smallest specimens only measured 

 14.50 mm. in greater diameter. No larger specimens than those 

 mentioned were found in the region, although the ground was well 

 explored for many years. 



The specimens were all found in crevices and hollows about the 

 roots of a clump of willows, growing in a marshy and boggy place. 

 Associated with them were numerous specimens of Polygyra mono- 

 don Rack., Succinea ovalis Say, Pomatiopsis lapidaria Say, Pyra- 

 midula striatella Anth., and other moisture-loving land shells. 



A comparison made with 48 specimens of P. multilineata from 

 Ohio, Michigan, and other localities, in my collection, showed great 

 difference in measurements. 33 specimens of this series measured 

 22 mm. to 24 mm. in greater diameter, and only two specimens 

 were as small as 21 mm. in diameter. 



The uniformity of size of the variety algonquinensis, the fact that 

 no other forms or sizes of the species were found in this region, and 

 the fact that they breed true, for the series was the result of three 

 years' collecting on the same small space of ground, entitles this shell 

 to varietal rank. And also, the perfect development of all the char- 

 acters, as found in the normal P. multilineata, and the fact that this 



