10 THE NAUTILUS. 



Sheik from flood-debris of the Rio Grande, Mesilln. 



Vallonia cyclophorella Anc. Pyramidula striatella Antli. 



Pupoides marginatus Say. Helicodiscus lineatus Say. 



" " variety. Zonitoides minusculus Binn. 



Bifidaria procera Gld. " singleyanus Pils. 



" hordeacella Pils. Limna?a humilis Say. 



" hebes mexicanorum Ckll.Planorbis parvus Say. 

 Pupa, blandi Morse. " umbilicatellus Ckll. 



Vertigo ovata Say. Physa, undet. Young shell. 



GaUinas River at Las Veycis. 



Vallonia cyclophorella Anc. Vertigo ovata Say. 



Bifidaria arm if era Say. Helicodiscus lineatus Say. 



" procera Gld. Zonitoides minusculus Binn. 



" hordeacella Pils. 



The species of principal interest is Planorbis umbilicatellus , not 

 hitherto known from the Rocky Mountain region south of Montana 

 to my knowledge. H. A. PILSBRY. 



TO WEST COAST CONCHOLOGISTS. 



Kind Friends : Nearly thirteen years have passed since I published 

 my little book entitled " West Coast Shells." It was issued with a 

 double purpose; first, to increase the interest of young people in the 

 study of conchology ; and secondly, to assist collectors in the work of 

 identifying their specimens. It is believed that both objects have to 

 some extent been realized. 



During these years students of conchology have not been idle. 

 Numerous new species have been brought to light, especially on the 

 southern coast, while the scores of intelligent collectors all over the 

 Pacific Slope have learned much concerning the haunts and habits of 

 well-known species. Eastern and foreign investigators and pub- 

 lishers have been busy also, and there has been more or less change 

 of names and classification. 



Repeated requests have been coming to me for a revised edition 

 of "West Coast Shells." I have delayed undertaking the work of 

 revision, partly from the pressure of other duties, and partly from a 

 desire to secure the latest and most complete information concerning 

 the shells themselves, and the most approved names by which they 



