lias been repeatedly described bu1 to be truly appreciated must 

 be actually seen: ii is beyond all comprehension. 



In a broad sense desert conditions are to aquatic tnollusks 

 (and likewise land molluscs! as abyssal conditions are to 

 marine molluscs. Such types naturally enough did no1 origi- 

 nate in these situations; they are the progeny of bold plastic 

 forms capable of withstanding the energetic physical condi- 

 tions which must be met by desert life. The sole reason why 

 peculiar desert types have not evolved to a more extensive 

 degree is due to the geologically-speaking temporary nature 

 of deserts. Abysses have existed since Life was first known 

 upon the earth, hence have developed a fauna all their own. 



BIBLIOGRAPHY. 



Arnold. R., 1903, The Palaeontology and Stratigraphy of the 



.Marine Pliocene and Pleistocene of San Pedro, California; 



Mem. Cal. Acad. Sci. Ill, 420 pp., 37P1. ; repriift as Contr. 



Biol. Hop. Lab., Stanford Univ. 



(Several freshwater species washed into marine terraces 



mentioned.) 

 Ashmun, E. II., 18!)!), Collecting in Arizona and New Mexico; 



Naut. XIII, 13-17. 



(Collecting notes, a few freshwater species are mentioned.) 



Baker, F. C, 1911, The Lymnaeidae of North and Middle 

 America, recent and fossil; Chic. Acad. Sci.. Spec. Pub. Ill, 

 539 pp., 58 PL 



(Several Lymnaea records chiefly compiled from the Litera 

 ture. The identifications are badly confused and few of the 

 localities correctly cited. The writer is quoted for several 

 entirely unknown to him.) 



Berry, S. S., 1908, Molluscan Fauna of the San Bernardino 



Mountains. California; Naut. NXI, 121-3. 



(Most of the records are extralimital.) 

 , 1909, The known Mollusca of San Bernardino County, 



California; Naut. XXIII, 73-9. 



(Only a partial idea of the freshwater fauna is suggested.) 

 Binney, W. G., I860, Land and Freshwater Shells of North 



America, I't. II I'ulmonata Limnophila and Thalassophila ; 



16] pp., numerous tigs. Pt. Ill (Operculates except Melan- 



oids), 120 pp. numerous figs. 



( Many interesting early records; the species then known are 



figured and described.) 

 Bowers, S., 1878, Geology of Santa Ros;i Island from Notes 



taken by Dr. Lorenzo G. Yates; 1901, Reconnaissance of the 



Colorado Desert Mining District Cal. Min. Bu. (special pub.) 



19pp. 



(A list of fresh and brackish water semifossils identified by 



Yates on p. 15.) 



1:: 



