112 THE NAUTILUS. 



Washington county is in the southwestern angle of Utah, 

 drained by the Virgin river, flowing into the Colorado. The 

 specimens are "dead" shells, but not fossil, I think. Accord- 

 ing to the label, Oreohelix strigosa was found in the same place. 

 The collector was not given for this or the preceding. 



All of the adult specimens of A. deserta have the last whorl 

 shortly free at the aperture. It is a senile form, probably ex- 

 tinct or on the verge of extinction, Amnicolidse lead a precarious 

 existence in the arid states. The rivers dp not afford suitable 

 stations. They have apparently never gained access to the 

 small perennial streams of the higher mountains; and permanent 

 springs and streams are so rare on the lower levels that the 

 colonies are small, few and widely separated. The large pro- 

 portion of extremely diminutive species in the arid region is 

 remarkable. It may, perhaps, be looked upon as a permanent 

 dwarfing due to unfavorable conditions. 



Figures of both species have been prepared, to be published 

 on a future plate. 



TWO NEW BIVALVE SHELLS FROM URUGUAY. 



BY WM. H. DALL. 



In a small collection of shells from Uruguay recently received, 

 among the marine bivalves were the following species which 

 appear to be undescribed. 



Glycymeris diaphorus n. sp. 



Shell subcircular when young, in the adult higher than wide; 

 the outer surface nearly smooth, with faint indications of obso- 

 lete radial ribs; the color whitish with reddish brown spots or 

 small maculations; beaks small, not prominent, prosocoelus; 

 the subumbonal area inequilaterally triangular, the anterior 

 portion very short in proportion to the posterior, about 1 to 3, 

 crossed by seven or eight diverging grooves and ridges; height 

 of the area about one-fifth its length in the adult; hinge with 

 ten or twelve teeth on each side, separated by a striated space; 

 in the adult a large part of the posterior series may be obsolete 

 or absent; anterior dorsal slope long and nearly straight, the 



