216 MOLLUSCA. 



long to many different genera. M. Cuvier has given indi- 

 cations of some of these, chiefly derived from the shape. 

 A few are furnished with an elevated crest or fin, as the 

 Thalia of Brown ; a few have both extremities rounded or 

 truncated, as Salpa octofera of Cuvier ; others have one ex- 

 tremity produced, as Holothuria zonaria of Gmelin ; and 

 even both extremities produced, as Salpa maxima of For- 

 skal. The Salapa moniliformis, so common in the Heb- 

 rides, and first recorded as a native by Dr. Macculloch, in 

 his valuable Description of the Western Isles, vol. ii. p. 188, 

 and imperfectly figured in its young state, at tab. xxix. fig. 

 2., appears to be closely allied to the S. maxima of Forskal, 

 and but very remotely with the S. poly erotica and confeder- 

 ata with which it is compared. This observer states, that 

 " It cannot bear to be confined in a limited portion of wa- 

 ter, as it died even in a ship's bucket in less than half an 

 hour." With us, in similar circumstances, those taken in 

 the evening were alive at noon on the following day. 



