516 SKELETON CRABS. 



resembles Bulla. I have no doubt, moreover, that occa- 

 sionally the lateral membranous expansions are horizontally 

 extended, and that the animal is enabled to swim in the 

 same manner, as I have mentioned, as peculiar to some of 

 the Bulla tribe. The Ancillarice crawl with a sliding 

 motion, and with considerable celerity. As they glide 

 briskly along, the tubular cylindrical siphon only is visible. 

 It is directed backwards and upwards, and sometimes is 

 laid flat on the back of the animal ; while the two trian- 

 gular lobes placed anterior to the foot, are extended 

 laterally, and in front moving about and exploring the 

 ground like tentacles, and no doubt serving the same 

 purpose. It is rather surprising that such an active Mol- 

 lusk as the Ancittaria, should have been apparently de- 

 prived by Nature of sight, no eyes being visible to my 

 observation in the specimens I kept alive. The species 

 which were dredged by us from a sandy bottom, and in 

 about fourteen fathoms water, were of a dirty-white colour, 

 with dull, brown, elongated, oval blotches, rather sparsely 

 and irregularly distributed. In the enormous size of the 

 foot, and its being prolonged anteriorly and transversely 

 lobed in front, and in the shell being partly concealed in 

 the body of the animal, Ancittaria resembles Natica. 



Among the pelagic skeleton Crabs may be ranked the 

 genera ErichtJtus and Alima, curious transparent shrimp- 

 like creatures, with spiny shields and elongated tails. I 

 have detected, among the number of those we obtained, 

 many new species. They are erratic and restless little 

 animals, and swarm on the surface of the Atlantic, when 

 the water is calm and tranquil. The Phronima, another 

 genus allied to them, is very frequently found inside the 



