50 PROCEEDINGS OF THE ACADEMY OF [Feb.; 



temporary freshening of the water. Hence it is not surprising that 

 certain strata in the lacustrine deposits contain numerous fossil 

 shells. Nearly all the species in this fossil fauna are still found 

 living in some part of the Bonneville Basin, as was long ago pointed 

 out by Call and Gilbert. The drainage during the overflow period 

 also afforded communication between the various rivers of the basin 

 and the Port Neuf River to the north, thus easily explaining the 

 observed similarity in their faunas. 



Our work in the region has developed a peculiar and as yet unsolved 

 problem in the breeding habits of the genus OreoheUx. The genus 

 is viviparous. In 1915 the snails of the genus collected in the last 

 week in August contained many embryos, but those obtained after 

 the first two or three days in September contained few or none. 

 In 1916 we found very few embryos during the months we were in 

 the field, June and July, yet if the embryos were to be so fully devel- 

 oped by the last of August as to be all gone early in Septeml^er, as 

 in 1915, it seems that they should have been developing by the 

 middle of July. To add to our perplexity, a considerable number 

 of live snails which were found among the dead shells in cleaning 

 them in November and December, nearly all contained embryos 

 of 1 1 or 2 whorls. These must have developed after July while the 

 snails were dormant. 



Over a large portion of the region covered by this report, the 

 combined effects of brush fires and overgrazing, with the consequent 

 erosion, have played sad havoc with the cover for land snails. In 

 some places where the steep slopes below clumps of bushes were 

 almost white with bleached OreoheUx shells, the washing of the soil 

 and dead leaves from beneath the shrubs had totally destroyed the 

 cover, so that not a living snail could be found, and the shrubs 

 themselves must die as erosion continues to take the soil away from 

 the roots. 



We have continued our station numbers from the 1915 expedition, 

 and revisited several of the 1915 stations to obtain more material 

 and data. We also include in this report some material oljtained 

 by Daniels in 1915 at Idaho Falls, Dubois, McCammon, and Weston,, 

 but not hitherto recorded, together with some unrecorded material 

 in the University of Colorado Museum, in order to keep all our 

 Utah and Idaho records together. 



We gratefully acknowledge the assistance of several who have 

 aided in the determination of difficult material. The Sphairiidae 

 were examined by Dr. V. Sterki. Dr. Bryant Walker has identified 



