364 W. J. CROZIER 



Alectrion (Ilyanassa) as example. Alectrion inhabits bottoms 

 of soft mud, very much hke those frequented by Conus so far 

 as the physical consistency of the substratum is concerned; but 

 on the other hand, Conus and Turbo (vide ante) are taken in 

 company on the same bottom, yet have quite cUfferent methods 

 of progression; hence little significance can perhaps be attached to 

 this correlation ; Turbo however, does not burrow as Conus does. 



The genus Xenophora comprises snails which exhibit the inter- 

 esting habit of reinforcing their shell with the dead shells and 

 skeletons of other organisms. To the rough surface thus pro- 

 duced, various living mollusks, corals, ascidians, worms, algae, 

 and so forth become attached, resulting in a shell mass which 

 Veighs in different cases from 150 to nearly 300 grams. The 

 foot itself is relatively small, measuring, when spread out for 

 attachment, about 2 cm. x2 cm., whereas the circumference of the 

 depressed conical shell-mass may be as much as 12 to 15 cm. 

 There is correlated with this disparity between the size of foot 

 and the size and weight of the shell a type of locomotion which is 

 somewhat remarkable and finds no place in the present classifica- 

 tion (of. Olmsted, '17) of pedal operations among gastropods. 



Xenophoras of apparently two species were obtained upon 

 muddy bottoms in 5 to 8 fathoms. The method of locomotion 

 must be observed from below, as the animal cannot creep up an 

 inclined surface (nor can it right itself after being turned over). 

 The foot is, when unattached, of a roughly dumb-bell outline, and 

 in life is covered with a thin layer of mud held by a slime secre- 

 tion. At its posterior end it carries the horny operculum. The 

 anterior part of the foot is compact and tough, with a firm an- 

 .terior margin. When the animal begins to creep, this anterior 

 part is the first to be applied to the substratum. Before the 

 foot is so applied, however, the anterior part of the animal's 

 body is thrust forward or to one side as far as possible. The 

 foot is then attached, beginning at its anterior margin and con- 

 tinuing with a smoothly 'flowing' motion until the whole foot 

 is in contact, but there are no perceptible pedal waves. The 

 central portion of the foot is then pulled sharply away from the 

 substratum, forming a very efficient sucker, since the anterior 



