ONCHIDIUM. 6 



observed by him in Bengal. Cuvier first clearly deve- 

 loped its structure, and published an elaborate memoir 

 on its anatomy. The species are almost all inhabitants 

 of tropical regions. 



O. Celticum, (Cuvier ?) Couch. 

 Plate F. F. F. fig. G. 



This most interesting addition to the British Fauna 

 was discovered by Mr. Couch, a naturalist who has 

 done much to extend our knowledge of the marine ani- 

 mals of the British seas, on the coast of Cornwall. He 

 found it abundantly on a confined space of rocks at 

 West Coomb, in Lantivet Bay, between Polperro and 

 Fowey, congregated in little groups, about a foot or two 

 from the surface of the sea, where the waves break 

 over them. These curious creatures ascend and descend, 

 so as to maintain their distance as the tides rise and 

 fall. They will not, however, bear long immersion in 

 sea-water. Cuvier, in the " Regno Animal," notices, 

 without describing it, an Onchidium under the name of 

 Celtiaim, from the coasts of Brittany. This was, very 

 probably, identical with Mr. Couch's species ; we there- 

 fore adopt, for the present, the name Celficum, as appro- 

 priate and significant. 



A living specimen, submitted to our examination by 

 Mr. Alder, measured rather more than half an inch in 

 length. Its form was oblong. Its cloak was of a black 

 hue, rather shining, thick and coriaceous, and covered 

 with short, thick, rounded tubercles, surrounded by 

 smaller ones ; the margin of the cloak considerably sur- 

 passed the foot ; the under side of the margin was 

 minutely granulated. The foot was oblong, and of a 



