48 PROCEEDINGS OF THE ACADEMY OF [Feb., 



HUNTING MOLLUSCA IN UTAH AND IDAHO IN 1916. 

 BY JUNIUS HENDERSON AND L. E. DANIELS. 



We were in Utah and southern Idaho from June 10 to July 24, 

 1916, eontmumg the work begun in 1915.^ More attention was 

 given to fresh-water species and the smaller land snails than before, 

 with some interesting results. A vast amount of work remains to be 

 done in this region before the molluscan faunas and the significance 

 of their present distribution are thoroughly understood. 



The known Tertiary and Pleistocene history of the Salt Lake 

 Basin is such that it must vitally affect the present distribution of 

 species, as well as possibly influencing local variations. Great Salt 

 Lake and Utah Lake, both within the area covered by this report, 

 are among the remnants of a much larger body of water known to 

 geologists as ancient Lake Bonneville. During Pleistocene time it 

 extended over a large part of Utah and into Idaho, with a depth of 

 hundreds of feet. In its retreat it left a fine series of terraces around 

 the margin of its basin to mark the various stages of its recession. 

 The formations deposited beneath the waters of the ancient lake, 

 the fluctuations of its water level, and its molluscan life as revealed 

 by the numerous fossils contained in the lacustrine deposits have 

 been subjects of extensive investigation and discussion.- 



The aridity of the vast area between the Rocky Mountains and 

 the Sierra doubtless dates well back into Pliocene time. The changes 

 in the water level in the various lake basins do not necessarily imply 

 periods of great humidity. Each receives the drainage of a large 

 territory, and being completely land-locked, a slight increase in the 

 precipitation for a short cycle may extend the borders of the lakes 

 far out over the flat, low-lying area around the lake margins, and 

 increased precipitation for a longer period may fill the basins to 

 overflowing. The rise and fall of the waters of land-locked lakes 

 constitute a complete and accurate record of the net result of all the 



1 Proc. Acad. Nat. Sci. Phila., LXVII, pp. 315-339, 1916. 



2 See especially the following: Gilbert, G. K., "Contributions to the History 

 of Lake Bonneville," U. S. Geol. Surv., 2d Ann. Rept., pp. 167-200, 1882, with 

 plates and map; "Lake Bonneville," U. S. Geol. Surv., Monographs, vol. 1, 

 1890, with plates and map. Call, R. Ellsworth: "On the Quaternary and 

 Recent Mollusca of the Great Basin, with descriptions of new forms," LT. S. 

 Geol. Surv., Bull. No. 11, 1884. 



