94 PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 



3.-;«EW MOfiM SCAIV FOKITIS FROU THE I>AR47IIE ATVB GUEEX RIVER 

 OROITP8, WITH DISCL'SS^ION OF SOME ASi^OCIATEU FOKITI!!! HERE- 

 TOFORE KIVOWIV. 



By C. A. TI^HITE. 



[Extract from the Annual Report of the United States Geological Survey for 1882, by permission of 



the Director. | 



Notwitbstauding the large number of specific and generic forms of 

 fossil mollusca that have been obtained from the Laramie and fresh- 

 water Eocene groups of Western North America, every fresh examina- 

 tion of those deposits in any region in which they occur is sure to add 

 somethiug to our knowledge of the fiiuna? which respectively charac- 

 terize them. While studying tbe Laramie Group in Northeastern Col- 

 orado during the season of 1881, I obtained no less than four new 

 species, and extended the known geographical range of several others. 

 Besides the new forms just mentioned I have recognized two others 

 among collections made by other i)ersoiis that have been in tbe National 

 Museum for several years past. All of these new forms are described 

 in the following paragraphs ; aiul remarks are made upon other forms 

 concerning which new facts have been discovered. These descriptions 

 are also to appear in the Annual Report of the United States Geologi- 

 cal Survey for 1882, in a " Review of tbe Non-Marine Fossil Mollusca 

 of North America." 



Genus UNIO Retzius. 



Unio clinopisthus (:*^). uov.), Plate III, tigs. 1 and 2. 



Shell transversely elongate, short in front of the beaks, elongate and 

 narrowing behind them to the posterior end ; basal margin having a 

 gentle sinuosity, there being a slight emargination just behind tbe mid- 

 length ; front margin regularly rounded ; dorsal margin i)roper rather 

 short; postero-dorsal margin forming a long, convex, downward slope 

 from the dorsal to the postero-basal margin, which latter margin is nar- 

 rowly rounded ; beaks depressed and ])laced near the i'ront of tbe shell. 

 A somewhat prominent, but not sharply defined, umbonal ridge extends 

 from the beak of each valve to the postero-basal margin, giving a flat- 

 tened space at the postero-dor.sal poi tion of each valve. Surface marked 

 only by concentric lines of growth. 



Length, 63 millimeters ; height, 30 millimeters ; thickness, both valves 

 together, 23 millimeters. (Museum No. 8359.) 



Position and locality. — Strata of the Green River Eocene group near 

 Washakie Station, in Southern Wyoming, where it was collected by Dr. 

 Havden. 



Genus CORBiCULA Miihlfeldt. 



Corbicula berthoiidi (sp. uov.), Plate IV, tigs. 1, 2, and 3. 



Shell very large, subtrigonal in marginal outline, moderately gibbous; 

 front concave immediately in front of the breaks; front margin regu- 



