''SLIPPER LIMPET" OR "BOAT SHELL." 407 



or highly arched, or concave, or twisted or short or long, as the 

 case may be. 



C. fornicata occurs on the shell-back or on the ventral 

 surface of the American King-Crab {Lwiulus polyphemus). 



In early stages the "Limpets" {C. fornicata) move about, 

 but when nearly half-grown they lead an irrevocably sedentary 

 life. They occur on muddy sea-bottoms in curious chains* of 

 often ten or twelve individuals, perched on the back of each 

 other — heads all in one direction. Such chains are often found 

 in which there is not a single male, and yet I have never found 

 an unfertilized female. 



The sexes are separate ; the smaller-sized males, as a rule, 

 lead a more roving life up to a certain age. 



Breeding season, early summer to mid-August. The eggs, 

 contained within a bunch of capsules (therefore analogous to 

 those of our British Whelk), are seen about midsummer. After 

 August absent, and instead clusters of spat are found within the 

 shell. Conklin believes that copulation occurs only once in a 

 lifetime. He found a seminal receptacle consisting of a con- 

 voluted tube within the female, and which at times was filled 

 with spermatozoa. The latter, therefore, mingles with the ova 

 before the egg- capsules are formed within the oviduct of the 

 female. 



The eggs of the several American species of Crepidula vary 

 remarkably in size. Those of C. fornicata (now a British 

 inhabitant) are nearly the smallest, although this animal is 

 the largest of the several species. In one bunch 55 capsules 

 were counted, and the eggs in each numbered 240, or a total of 

 13,200 to a single female. 



The ** Slipper Limpets " are supposed not to be increasing in 

 numbers in American waters (?). 



Kegarding Conklin's elaborate researches into segmentation 

 of the ovum of Crepidula species and the dwarf race of C. plana, 

 these are aside from the purport of the present paper. 



Their British Introduction and Eesults. 

 It may be inferred from what precedes that up till within a 

 comparatively recent date couchologists had never met with nor 



* The " windrows " of some American writers. 



