THE PYRAMIDELLID M0LLUSK8 OF THE OREGONIAN 

 FAUNAL AREA. 



By William Heale:y Dall and Paul Bartsch. 



0/ the Diiision of Mollusks, U. S. National Museum. 



INTRODUCTION. 



The completion of the nionooraph of West American Pja-amidel- 

 lidte upon which the authors of the present paper have for some years 

 been at work, being delayed by various causes — though in large part 

 long ready for the printer — it was thought best to select from it, for 

 immediate publication, the portion relating to the Oregonian fauna, 

 which to a considerable extent is complete in itself, pending the com- 

 pletion of details relating to other faunal areas of the coast. 



For the purposes of the present paper, subject to future modification 

 with greater knowledge, the fauna here named Oregonian extends from 

 the northern limit of the Alexander Archipelago southward along the 

 coast to Point Conception, California. The limits of any fauna are 

 never quite absolute, there is alwaj's a partial merging of the periph- 

 eral population with that of the adjacent faunal areas, but the pro- 

 portion of Pyramidellid species in the present case, which are held in 

 common with the faunas northwest and southeast of that here called 

 Oregonian, is noticeably small. 



Attention is called to the fact that it is a" Pyramidellid fauna which is 

 here discussed. The general moUuscan fauna, still more the general 

 invertebrate fauna of the coast in question, may or may not even- 

 tually be found to agree in distribution with our Pyramidellids. That 

 is a question which we are not ready to decide at the present time and 

 which will demand much more time and study than it has yet been 

 possible to give to it. 



Collections over this long stretch of coast, comprising some 22 degrees 

 of latitude, or more than 1,300 geographical miles, have naturally been 

 concentrated at the most accessible points, while there are long 

 stretches of coast without harbors where as yet no collections what- 

 ever have been made. Neglecting the deep-sea dredgings, which have 



Proceedings U. S. National Museum, Vol. XXXIII— No. 1 574. 



491 



