254 VALLONIA. 



horizontal direction to the very margin of the lip. The number of 

 ribs was found to be from 23-35 in the type. Some forms differ so 

 much that they are to be considered varieties : 



Var. HELVETICA Sterki, n. v. 



Small ; glossy, transparent, colorless ; shining, without membra- 

 nous ribs, in their place fine stride being visible, more from their 

 white color than from being prominent. Umbilicus rather regularly 

 spiral. Greater diam. 2*2 mill. A very peculiar and beautiful 

 form. 



Jura Mts. near Brugg, Switzerland, and in drift on Aare river, in 

 company of typical F. costaia. 



Var. AMURENSIS Sterki, n. v. PI. 33, figs. 50, 51, 52. 



Small ; spire nearly flat ; deep horn colored ; ribs strong and dis- 

 tant, about 22 on the last whorl, the back of which is very little or 

 not at all deflected in front. Umbilicus rather regular, wide, per- 

 spective from the first volutions. Greater diam. 2*2 mill. 



Kassakewitsch, on the Amur. 

 Var. PYRENAICA Sterki, n. v. 



Large; umbilicus wide, perspective; whorls 4, more gradually 

 increasing than in the type, the last less expanding to the aperture ; 

 ribs small. There is an obtuse angle in the circumference-outline 

 about one-fifth of a volution behind the aperture. 



Greater diam. 2'6-2'8 mill. 



Pyrenees (in a lot with typical costata.) 



Var. MONTANA Sterki, n. v. 



Rather small; rather thick, colorless, translucent, spire more 

 elevated verv low conic ; surface with rather crowded rib-striae, not 



/ ' ' 



membranous. Last whorl gradually ascending to the aperture, then 



the suture descending ; lip very thick. 



Rocky Mts. 



Possibly these varieties will have to be ranged elsewhere when more 



O 



and fresh specimens come to hand. 



V. PARVULA Sterki, n. sp. PI. 32, figs. 23, 24, 25, 26. 



Widely umbilicated, quite flat above, or with little prominent apex, 

 thin, horn colored, with rather fine, dense membranous ribs, and 

 finer strise between them ; nucleus with microscopic revolving lines. 

 Whorls a little over 3, slightly flattened above and below the 

 periphery, with a deep suture, the last comparatively wide, rather 



