more than a playa or temporary marsh kept submerged by 

 artificial damming, drains abruptly by a steep narrow gorge 

 rapidly encroaching upon it, Bear Gulch, into the Santa Anna 

 Canon, thence to the San Bernardino Valley. The fauna of 

 the Santa Anna Canon, Mill Canon, and other streams flowing 

 into the San Bernardino Valley from these Mountains is typical 

 of the Los Angeles System and has already been listed. _ That 

 of Bear Valley and the streams and cienagas emptying into it 

 is entirely distinct, however, but finds close affinities with the 

 fauna of the Mojave System. The species obtained by the 

 writer during a visit in 1910 follow; those marked by an 

 asterisk are absent from the Los Angeles System. 



Musculium lacustre (M filler) 

 Corneocyclas pulchella (Jenys) 

 *Corneocyclas sp. now 

 *Lymnaea palustris (Midler) 

 Lymnaea solida cubensis (Pfeiffer) 

 Planorbis trivolvis (Say) 

 Segmentina parva (Say) 

 "Segmentina dilatata (Gould) 

 Physa fontinalis acuta (Draparnaud) 

 Valvata tricarinata (Say) 



Since the Systems or faunules are founded ' not on 

 drainage areas but the fauna contained, the writer has felt 

 obliged to treat this valley as an integral part of the Mojave 

 System rather than of the Los Angeles into whch it partially 

 drains. As long as Bear Gulch is a precipitous gorge, prevent- 

 ing the immigration of the Los Angeles forms, and the valley 

 below hot and arid, preventing the emigration of the Bear 

 Valley species, a mingling will hardly take place readily. 



CONCLUSIONS. 



A noticeable feature in the study of the acquatic Mollusca 

 of southern California is the infrequency of species and genera 

 peculiar to lakes, Paludestrina protea constituting a note- 

 worthy exception, due to the arid or desert nature of the 

 country which has contributed heartily to the extermination 

 of such forms if they were ever present or became introduced. 



The fauna numerous in individuals but constituting only 

 a few species which inhabited the former Lake LeConte now 

 the more depressed portions of the Colorado Desert is of inter- 

 est showing the adaptation of local species to temporary cir- 

 cumstances. For many years it was supposed that several of 

 these, particularly Paludestrina protea, were totally extinct. 

 Careful field-studies have proven the existence of each and all, 

 however, in isolated situations to which they were restricted 

 upon the drying up of the basin. The vast almost unlimited 

 wealth of molluscan life which formerly existed in that region 



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