notes on chrysodomus and other mollusks 

 fro'm the north pacific ocean. 



By William He ale y Dall, 



Honorary Curator of MoUvHks, Unitcfl States Notional Museum. 



During the past year the writer received from Mr. Y. Hirase, of 

 Japan, a number of shells for identification, with a request that any 

 new species be described. Having given special attention to the 

 Chrysodomoid whelks, the opportunity was taken to revise the group- 

 ing of those mollusks as well as to prepare descriptions of a number 

 of new species which occurred in Mr. Hirase's collection. 



The unique types were returned to him, but of several speoies 

 cotypes were available for the National Collection. A few species 

 of especial interest from the west coast of America are included in 

 this paper. 



A prodrome of the proposed classification of Chrysodomus and 

 its allies was published^ but, as this comprised merely a list of 

 genera and subdivisions with designation of types, it was thought 

 best to give hercAvith the complete discussion of the facts upon 

 Avhich the revision was based. A large number of boreal species 

 from the Bering Sea region remain to be described at a later oppor- 

 tunity. 



Genus CHRYSODOMUS Swainson. 



The nuclei or larval shells of species belonging to Chrysodomini 

 and its allies present several distinct types and numerous mutations. 



In many cases, as in Buccinum and Busycon^ it was shown many 

 years ago by Loven and others that a single ovicapsule contains a 

 number of ova fertile and unfertile. The unfertile eggs serve as food 

 for the larvae developed from the fertile ones and there is a certain 

 amount of competition between the larvae in the capsule which re- 

 sults in the most vigorous larvae getting more food and making a 

 huger growth than the more weakly coinhabitants of the capsule. 

 Thus at the time of leaving the capsule and coming into the outer 

 world, it sometimes happens that there will be perceptible differ- 

 ences between the individuals issuing from a single capsule, not only 



1 Proc. Biol. Soc. Washington, vol. 29, pp. 7-8, January, 1916. 



Proceedings U. S. National Museum. Vol 54— No. 2134, 



207 



