10 



THE NAUTILUS. 



shouldered above the median keel. Covered with an olive epi- 

 dermis. Surface marked by delicate growth-lines and excessively 

 fine, close spiral stria?. Alt. 5-2, diam. 3 mill ; alt. of apert,, 2, 

 width 1-3 mill. 



Lake Patzcuaro, West Mexico. 



This species is very different from other American Amnicoloids. 

 (To be continned.) 



DESCRIPTION OF A NEW SPECIES OF HYALINA. 



BY WM. H. DALL.' 



Dr. V. Sterki, of New Philadelphia, Ohio, has of late years been 

 giving special attention to the minute forms of Pulmonata, Vertigo, 

 Papilla, Hyalina, etc. In 1886 he collected a small Zonites, of the 

 section Hyalina or Conulus, which, being submitted to several 

 naturalists, appeared to be a new species, although of remarkably 

 small size. In 1887 a few more specimens were obtained, which 

 he has submitted to me with the request that I describe them. 



Shell minute, thin, yellowish translucent, brilliant, lines of growth 

 hardly noticeable, spire depressed, four-whorled ; whorls rounded, 

 base flattened, somewhat excavated about the cen- 

 ter, which is imperforate; aperture wide, hardly 

 oblique, not very high, semilunate, sharp edged, 

 the upper part of the columella slightly reflected ; 

 upper surface of the whorls roundish, though the 

 spire as a whole is depressed. Max. diameter 0.044 

 inch (line a— b, Fig. 1) ; alt. 0-026 inch. 



This little shell is clearly not the young of a 



Papilla or of any of our other small Zoniies. It 



is certainly the smallest American species. H. 



parvula Rang, from Cape Verde Islands, has a 



little less diameter, but is higher in the spire. 



C>N H. pygmcea and H. minutissima Lea are decidedly 

 ^^'^^ZL^ larger, besides belonging to a different group. It 

 is probably one of the smallest species known, and remarkable for 

 its imperforate umbilicus. 



1 From Proceedings U. S. National Museum, vol. xi, 1888, ]x 214. 



