19 



outer rocks exposed to the ocean surf have short-spired rela- 

 tively smooth, wide-mouthed shells, which afford the least 

 leverage to the waves. For washed from his perch and carried 

 to the muddy bottom off the shore by the undertow, an adult 

 Nucella can hardly survive; and those offering the least fric- 

 tion and having the stronger hold on their situs are most likely 

 to survive. There is also a connection between the situs and 

 the shell which is less easily explained, and that is that, on 

 rough surfaces such as an "oyster reef," or bar, the specimens 

 of /^m^//ojfl are almost unanimously rough and laminate, while 

 in undisturbed water on rocks with sandy surroundings the 

 finest and most delicate development of lamellae and crenu- 

 lations is to be found, according to collectors. In all cases 

 Nucella seems to prefer a rocky habitat, especially if it affords 

 young oysters or other sessile or sluggish species serving it as 

 food." 



At another point in the same paper Dall ( p. 563-564) hints 

 at the idea that inheritance may play a part in determining 

 the character of the local races, where he remarks:- ** This 

 species {lamellosa) submits to such changes, incident to situs, 

 that single specimens, or even numerous specimens from single 

 localities, might be taken for different species, especially as 

 specimens from a single locality often exhibit a singular uni- 

 formity of characters, even in factors which would seem not 

 likely to be subject to influences of the environment, such 

 as the number of the major spirals. These uniformities are 

 probably due to inheritance from a common ancestor." 



The above paper by Dill was primarily taxonomic in char- 

 acter, and was based largely upon 549 specimens in the U.S. 

 National Maseum. His account of the ecology of the species 

 was rather incidental, and was based partly upon his ownob- 

 seavations made in Alaska and partly on information received 

 from his correspondents on the Pacific Coast. His views were 

 no doubt markedly influenced by the interpretation presented 

 by Cook<: upon the allied form inhabiting the North Atlantic. 



