1016 On the Shells of the Colorado Desert [Oc 
ing at most but more or less colonial or local varieties of 
same general form, if 
The species of Physa heretofore credited to the southern 
credits it to ‘‘ Pecos river, Texas,” but why Texas I have beet 
unable to discover, as the Pecos is a stream several hun 
miles in length, extending from its tributary sources in 
southerly subranges and lower flanks of the Rocky mou 
tending in fact, in part, farther east than the easterly flank or" os 
hills of the Rocky mountains, and discharging on the easterly 
Atlantic side of the continent into the Gulf of Mexico. oe 
occurrence of any of these forms which have been regarded 2 
belonging to the fauna of the Pacific coast regions, with which 
are familiar and to which your attention has been her | tae 
directed, within the area of more easterly faunal domains, ee 
a most important significance as related to the variation 
identity of species, and still more in its bearing upon the r ae 
of faunal characteristics and specific characters to environs 
conditions, 
Still further to the east we have the Colorado of the | 
or the Colorado of Texas (or little Colorado) as it 18 Vana i 
called, which also empties into the Gulf of Mexico, anc 
an area estimated at 38,000 square miles, extending north-wes : 
toward the drainage basin of the Rio Pecos to the table p 
New Mexico and Texas, the Staked Plain so-called, oF 
1L. and F. W. Shells of N, A. 
? Geographical Catalogue, April, 1867, species 368, 369- 
