32 Quarterly Journal of Conchology. 



(T. Sowerhyi)^ and Chlorostoma crawling over the sedimentary rocks, 

 upon -which grows the green Cladophora, or some allied vegetable form 

 upon which it feeds, and which also is the favourite food of several 

 species of limpets. 



The order of Scutibranchiata, according to the Adams's, includes 

 the families of Neritidce (none of which are found in the Californian 

 and Oregonian province, though they begin to appear on the coast of 

 Lower California) ; and the Trochidcc, which is largely represented by 

 the following genera : Eiitropia, one species ; Lepotliyra, three species ; 

 Pachypoma and Pomaulax, one species each; Liotia, one (perhaps two) 

 species ; Thalotia and Trochiscus, one species each ; Calliostoma, 

 Chlorostoma, Omphalius, Margarita, and Gibbula, each by several 

 species. 



The family of Haliotidce, which is represented by several species all 

 of lai-ge size, widely distributed, and exceedingly numerous in indivi- 

 duals ; Fissurella including Lucapina, Glyphis, and Clypidella, also 

 Puncturella and Emai^ginula. 



Dentaliadce by two or more species ; Tecturidce by several species 

 of Acmwa, also by Scurra ; Gadinia by one, and Nacella by six or 

 more species. 



Chitonidoi by numerous species and great numbers of individuals. 



It may be that some of the groups included by the Messrs. Adams 

 in the order referred to, as our knowledge increases will require to be 

 separated or removed, but so far as the purposes of comparison as 

 made herein are considered, the result will not be materially impaired. 



The total number of marine molluscan species and well-marked 

 varieties within the Californian and Oregonian province, so far as 

 known and determined, is not far from 630, of which 200 are bivalves; 

 and of the remaining 430, 123 are included within the Scutibranchs. 

 Of this latter number, about 40 belong to the Chitonidce, and the same 

 number to the Troclndce. 



Of the 247 gasteropods enumerated by the late Dr. Stimpson in 

 the Smithsonian Institution Check-list, as found from the Arctic Seas 

 to Georgia, 32 only, or less than one-eighth, come within the order 

 mentioned. Of this comparatively small number, seven (7) are Chitons, 

 and fourteen (14) belong to the TrocMdce, while Halintis* is without 

 a representative. The Trochidoi within this province are not repre- 

 sented by such marked or unique characters as distinguish their 

 relatives on the west coast. 



Some revision may be required hereafter in the number of Scuti- 

 branchiato species credited to the west coast province, as forms now 

 catalogued as distinct may in some instances be united ; but, on the 

 other hand, it is not unlikely that new forms undoubtedly distinct will 

 be detected when the coast is more thoroughly explored. 



* A solitary specimen of BaUotis, of small size, was obtained through dredging 

 in the Gulf Stream, four or five years ago, by Count L. F. Pourtales, of the U. S. 

 Coast Survey, but south of Georgia. 



