1893.] NATURAL SCIENCES OF PHILADELPHIA. 277 



A. Aperture rather circular, surface with membranous ribs (rarely 

 smooth, with fine strise in place of ribs) 



1. Of medium size or small, pale or reddish horn colored. 



a. Of medium size (average 2 - 5 mm.) last whorl usually a little 

 descending in front costata. 



aa. Small (2 mm. or less), back of last whorl not descending. 



parvula. 



2. Rather large (2 - 7 mm.) whitish ; riblets membranous, very fine 

 and crowded albula. 



B. Aperture transversely elongate ; superior margin much less curved 

 than inferior. 



1. Rather small (2%3 mm.) and thin shelled, with fine membranous 

 ribs, light grayish, transparent; lip moderate tenera. 



2. Rather stout (diam. 2'6 mm.), with ribs on the shell without 

 membranous appendages ; lip strong, white gracilicoda. 

 a. Last whorl not descending ; umbilicus very wide ; diam. 2 



mm.; otherwise like group III, surface with membranous 

 ribs ' patens. 



Group III (of cyclop hovel la). Aperture transversely elongate, 

 elliptic or pear-shaped, inferior margin more curved, but not angu- 

 lar; last whorl descending in toto after ascending previously ; peris- 

 tome moderately everted, without a lip (as a rule). 



A. Small, diam. 2 - mm. or less; horn colored; umbilicus very 

 wide, perspective, surface with membranous ribs, peristome con- 

 tinuous persjjectiva. 



B. Larger, with very fine crowded ribs, or almost smooth ; peris- 

 tome not continuous. 



1. Diam. 2"4— 2*5 mm.; whorls 3; very finely rib-striate 



mionecton. 



2. Diam. 2-6-3-3 mm; whorls 3-1-4. 



a. Diam. 2*6-2 - 8 ; surface with fine, somewhat irregular, 

 crowded membranous ribs ; color grayish-white to grayish- 

 horn (rarely with a thin white lip) cyclophorella. 

 aa. diam. 3 - or more ; surface finely ribbed 



b. spire rather elevated ; diam. 3 mm. tenuilabris. 



bb. spire little elevated ; diam. 3'5 mm. ladacensis. 



TABLE OF GEOGRAPHICAL DISTRIBUTION. 



1. V. pulchella Mull. : circumboreal (eastern Asia? Pacific 

 slope of North America?) Australia, Mauritius (introduced.?). 



2. V. excentrica Sterki : all Europe ; eastern North America. 



