somewhat surprising to find over fifty species, only nine of which had been hitherto known to exist in the Central Province, where an extreme "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 reprinted 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[1] to that portion of the United States embraced between 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 conditions were present, and some species had a very local distribution.
The eastern slope of the Snowy Range is abrupt, and receives comparatively 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 numerous on the Sierras in the southeastern corner of the Territory, where Pupilla 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 astonishing 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 mountaintops, is strange. This Microphysa was afterward met with in 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,
- ↑ In the "Bulletin of the Museum of Comparative Zoölogy" (Cambridge, Mass.), vol. iii.,No. 9, "Geographical Distribution of North American Mollusca."
