MOLLUSCA. 317 



I WILL now proceed to the other classes of Invertebrata which 

 remain to me. 1 shall not attempt any definite order in arrange- 

 ment, nor pretend to any thing like completeness, or authority in 

 the details. I shall present the objects in natural groups, giving 

 their nomenclature according to the latest authorities, with such 

 remarks upon some of them as have been suggested to me from 

 books, from correspondents, and from personal observation. 



And first, we have remaining other classes of Mollusca, none 

 of which, hitherto found, with a single exception, form shells. 



Class CEPHALOPODA, Cuvier. 



The body of these animals is composed of a muscular sac, en- 

 closing the viscera, having the mouth at one end, which is sur- 

 rounded by long fleshy arms, of various shapes. Along these 

 arms, at intervals, are little cups, by which the animal is capable 

 of adhering, with great tenacity. With them it seizes its prey. 

 It also uses them in crawling from place to place, or as oars to 

 propel itself. 



Spi'RULA PeRO'NII, Lam. Nautilus spirula, Lin., Blainv. ; J»/aZa- 

 coL, pi. 4, f. 1. Enajc. Mith., 465, f. 5. 



This is the only species of the genus known. It inhabits the 



open sea, and is sometimes found, after storms, upon the shores of 



Nantucket. The shell is white and pearly, coiled up in two or 



three turns which do not touch each other, something like a ram's 



horn. The surface exhibits constrictions, at short intervals, each 



of which corresponds to an internal partition, so that the whole 



shell is divided off into chambers, having a tube, however, at one 



side, so that the whole are in communication. 



Of the very curious and minute Nautilacea, so many of which 

 have been found about the British Islands, there are doubtless 

 many among the sands of our shores ; but none have as yet been 

 detected. 



