GEOLOGICAL SURVEY OF THE TERRITORIES. 467 



II.— REPORT ON MOLLUSCA. 



By S. E. Eoberts, 

 Recorder Conchological Section, Academy Natural Sciences, Philadelphia. 



The following list comprises the mollusca collected by Professor F. Y. 

 Hayden while engaged in the various geological surveys made under 

 direction of the Department of the Interior. An examination of this 

 list will show that most of the species named are common not only to 

 the districts watered by the Ohio and Mississippi Eivers, but also to 

 many other sections of the North and East, thus showing a widespread 

 distribution of nearly all the species which are abundant in the more 

 eastern portions of the United States. This is the more curious, par- 

 ticularly among the fluviatile mollusks of the Upper Missouri, for there 

 the rivers belong to a different system of drainage. 



Of the land shells the species Helix haydeni, Binney, which was col- 

 lected in large numbers at Weber Cation, Utah, is interesting from the 

 fact that it belongs to an entirely different sub-genus from any previously 

 known to this country, it being very closely allied to the Madeira genus, 

 Tectula, Lowe. 



Dr. Hayden collected more than fifty specimens of different ages, all 

 of which were somewhat bleached. 



This species was found associated with Helix cooperi, Binney, many 

 specimens of the latter being also obtained. 



At Falls City, Nebraska, a small shell was found near the size of Helix 

 bucculenta, Gould, but with a closed umbilicus. It is probably a small 

 variety of H. albolabris, Say, and has been so labeled in the collection , 

 of the Philadelphia Academy of Natural Sciences, where the specimens 

 are deposited. 



Among the fresh-water shells only one species of the family Vivipari- 

 dffl, the Melantho integra, Say, has been noticed. This was collected in 

 the Big Sioux Eiver, Nebraska. 



Pomatiopsis lapidaria, Say, belonging to the Amnicolidce, was found 

 at Fort Berthold, in Nebraska. This is the most western locality known 

 for the species. 



In addition to the number of species belonging to the family Unionidce, 

 common to the Northern and Western States, there will be noticed three 

 southern species which were collected at Falls City, Nebraska. These 

 are Unio nigerrimus, Lea, U. Bitter svillmisis, Lea, both belonging to the 

 Texan fauna, and the Unio Mississippiensis, Conrad, which was described 

 from specimens obtained in Mississippi. Unio Topeheensis, Lea, a Kansas 

 species, was also found here, while at Nebraska City a perfect valve 

 of Unio pressus, Lea, was obtained. This species belongs to the great 

 lakes, sometimes occurring as far east as the Erie Canal, New York. 



The fact of there being no Melanians in the list confirms the state- 

 ment made by George W. Tryon, jr., in his monograph of the Strepoma- 

 tidw (in the Amer. Jour. Conch., vol. 1, p. 125,) that these shells do not 

 occur west of the Mississippi Eiver, except in the rivers of the Pacific 

 States. 



The list of species is not as complete as might have been expected,, 

 but future explorations will no doubt bring to notice many additional 

 forms which are to be found in more eastern localities. 



