44 THE POPULAR SCIENCE MONTHLY. 



somewhat surprising to find over fifty species, only nine of which had 

 been hitherto known to exist in the Central Province, where an ex- 

 treme " paucity of species, .... owing to the nature of its climate 

 and soil," had been alleged. Five of these species were new to science, 

 and have since been described in the " Bulletin of the United States 

 Geological Survey," second series, No. 2, which has since been re- 

 printed in an extended and revised form, in the Annual Report of the 

 Survey for 1874. 



The Central Province alluded to above is the name given by Mr. 

 W. G. Binney ' to that portion of the United States embraced be- 

 tween the crests of the Sierra Nevada and Cascade Mountains on the 

 west and the edge of the great plains on the east. It was considered 

 to be unfavorable to the development of pulmonates and deficient in 

 the number of species to be found, and that its fauna was closely 

 allied to that of the Eastern States, whence it had been largely derived 

 by way of the north, where the plains are succeeded by forests and 

 the Rocky Mountains dwindle into hills. 



With respect to this distribution of mollusks in Colorado, none were 

 found on the eastern slope of the range, although there is no conclusive 

 evidence that they do not exist there ; altitude seemed to have very 

 little influence upon their dispersion, as long as other favorable con- 

 ditions were present, and some species had a very local distribution. 



The eastern slope of the Snowy Range is abrupt, and receives com- 

 paratively little rain. Westward of the summit, however, certain 

 genera as Zonites, Vitrina, Vallonia, Patula, Pupa, Succinea, and 

 Pisidium were everywhere represented. Vitrinas and pupas were, 

 perhaps, the most common forms, the latter being particularly numer- 

 ous on the Sierras in the southeastern corner of the Territory, where 

 Papilla alticola were traced up to the very limit of timber-growth, 

 and upon the face of precipitous cliffs of volcanic rock, in whose clefts 

 only tufts of grass could gain a foothold. With the latter shell also 

 occurred some small succineas, and a mollusk with a delicate, box- 

 shaped shell, only one-tenth of an inch in diameter. Plenty of these 

 little fellows, as lively as could be, were to be found at the astonish- 

 ing height of 11,500 feet. They proved to be undescribed, and to 

 belong to the sub-genus Microphysa, the two American species of 

 which, heretofore known, are natives of the Gulf coast and the West 

 Indies. Why this species should depart so far from the habits of its 

 congeners as to thrive best in the arctic climate of these mountain- 

 tops, is strange. This Microphysa was afterward met with m the 

 valleys south of these Sierras, and in the mountains west of North 

 Park. In this same southern group of mountains many other shells 

 were found at a lesser altitude, but where water froze every night in 

 August of the same species as existed in other parts of the Territory, 



1 In the " Bulletin of the Museum of Comparative Zoology " (Cambridge, Mass.), vol. 

 iii.,No. 9, "Geographical Distribution of North American Mollusca." 



