1922] NATURAL SCIENCES OF PHILADELPHIA 75 



With the exception of the small and in many respects peculiar 

 species which is described in the present paper from Whitewater 

 Canyon, the desert helicoids seem invariably to occupy the same 

 sort of situations and to have essentially similar habits. They 

 have not yet been discovered deep down in rockslides like so many 

 of the Arizonian species, but generally aestivating under blocks 

 and boulders of granite, or among the loose soil and rubble in the 

 crevices thereof. When active they frequently come to the surface, 

 where at favorable moments they may be found in the open, 

 crawling. Beyond this little is known of their habits, their food 

 supply, or their position in the general bionomic economy, as is a 

 natural sequence of the fact that without any doubt the very 

 great majority of existing species are still unknown to us in any 

 way whatsoever. 



The distribution of the desert palm. (Neowashingtonia filamentosa) 

 has been plotted out with a view to showing its probable relation- 

 ship to the ancient shore line of the Gulf of California which seems 

 to have extended well up into this basin at no very distant period. 

 Whether anything of the sort will be possible with the land snails 

 remains to be seen, but it is at least an interesting speculation 

 whether the characteristic desert Eremarionta was not itself, at one 

 time, a maritime group as the more typical section of Micrarionta 

 still remains to this day. 



Of the numerous North American groups of land snails smaller 

 than the helicoids, none appears to have been recorded from the 

 area under discussion hitherto. 



Freshwater Mollusca. — In nearly complete contrast to the 

 land snails, interest in the fresh-water Mollusca necessarily centers 

 almost exclusively in the relict-covered bed of the ancient Lake 

 Cahuilla, in other words, the Colorado Desert in the exact original 

 sense of that term. The wonder caused by the enormous numbers 

 of the stranded shells which fill the soil in many parts of the valley, 

 and the interest aroused by the eventual discovery of many of the 

 same species still flourishing in certain of the outlying springs and 

 rivulets has long attracted attention to this part of the fauna. 

 The pioneer publication dealing with a fresh-water mollusk of this 

 region was probably that of Lea ('52), who described his Anodonta 

 Calif orniensis from the "Rio Colorado, California." A few years 

 later Gould ('55) applied names to five species of fresh-water 



