286 PROCEEDINGS OF THE ACADEMY OP 



Included in the collection are two specimens of the genus 

 Trijonia, Stimpson. This curious little genus was heretofore 

 considered to be restricted to the Colorado Desert of southern 

 California, where, in a fossilized condition, it exists in such num- 

 bers as frequently to cover the surface of the ground. Two 

 species have been described, viz., the type T. (Melania) exigua, 

 Conrad, of which Melania protea, Gould, is a synonym, and 

 Tryonia clathrata, Stimpson. The two Utah specimens are 

 probably T. exigua. 



The genus Tryonia is included in a group of very small species 

 of Amnicolidffi, having the whorls oruameuted by ribs, nodules, or 

 spines; it includes the genera 



Faludestrina, Orb., 1841. West Indies and S. America. 



Pyrgula, Crist and Jan. 1832. Europe.* 



Fotamopyrgus, Stimpson, 1865. New Zealand. 



In addition to the above, the collection includes Succinea 

 lineata, W. G. Binney, Linmaea pa/usirts, Miill., L. stagnalis, 

 Linn., and L. desidiosa, Say, Physa elhptica. Lea, and Planorbis 

 trivolvis, Say ; the latter very large specimens with the margin of 

 the aperture expanded like those from the St. Lawrence River, 

 described by Mr. Whiteaves as PL macrostomus. 



' Mr. John Wolf has described Pyrgula scalariformis, from the post 

 pliocene near Tazewell, Illinois River. Other minute species may be de- 

 tected hereafter, when our rivers are more carefully explored, as in France 

 a number of new species have rewarded the minute research of recent 

 collectors. 



