iiEroRT o:n^ the imollusks collected by the INTER- 



^^ATIONAL BOUNDARY C0MM1SSI0:N" OF THE UN^ITED 

 STATES AND MEXICO, 1892-1894. 



By William Healey Dall, 



Uonorartj Curator of the Department of Mollushs. 



\ 



Introductory remarlxS. — In the report of the first Mexican Boundary 

 Survey, with Captain (afterwards General) W. H. Emory, U. S. Army, 

 ill command, no account appears of moHusks collected. Much space is 

 <;iven to the vertebrates, botany, andgeology, and admirable illustratious 

 adorn the several reports, but it is probable that no great number of 

 mollusks was collected and the specimens obtained were overlooked 

 or scattered. 



It has long been known that the region north of Mexico, between the 

 Rio Grande and the Colorado, is faunally distinct from the region of 

 the Atlantic drainage, as well as from the fauna of the Pacific Coast. 

 It has been named as a faunal region by several students of geograj)li- 

 ical distribution, and among students of mollusks has been usually 

 termed the Central or Sonoran faunal region. So far as these animals 

 are concerned, it seems rather a i^rolongation northward of the fauna 

 of the mountains of northern Mexico than a southern extension of 

 that of the Great Basin west of the Rocky Mountains. It i^resents 

 features due to contributions from the (^^alifornian and Mexican re- 

 gions, the latter predominating, with a few stragglers from the North. 

 Seldom visited, arid, and inhospitable to molluscan life, the data relat- 

 ing to its fauna are widely scattered and mingled with those which con- 

 cern those of other parts of the western country. It may, therefore, be 

 useful to recall the names of those to whom, in the i^ast, aa e have been 

 indebted for collections made in the region, and to give a brief notice 

 of the principal sources of information in the literature. 



Some of the first shells described from this region formed part of a 

 collection made by Berlandier, and were sold by him to Lieutenant 

 (afterwards General) D. N. Couch, U. S. Army, of the original boundary 

 survey, who generously presented them to the Smithsonian Institution. 

 These were named by Dr. Isaac Lea in 1857, but appear to belong to the 

 relatively low-lying region east of the Sierra Madre in the States of 



Proceedings U. S. National Museum, Vol. XIX— No. 1111. 



333 



