236 SHELLS AND SHELL-PISH. PART I. 



as Chelinotus is of this : such, at least, are our present 

 impressions on the relations of these perplexing forms. 

 Our object, in all cases where we cannot analyse, is to 

 state difficulties, not to smooth them. The present 

 instance is one of the few groups we are compelled, 

 from this cause, to leave in uncertitude. The reader 

 will remember that the same difficulty has occurred in 

 regarding the Bullce. Now, both of these are analogous 

 groups, and, with the Natlcce, are all representatives of 

 the naked order TECTIBRANCHIA. This will be ap- 

 parent on looking to the opposite columns, the contents 

 of which follow each other perpendicularly, while the 

 analogies are expressed horizontally. 



(218.) A chapter would be scarcely sufficient for the 

 full explanation of the innumerable relations implied in 

 this table ; we must therefore confine our attention to 

 that line which contains the analogical representations of 

 the Tectibranchia. All these turn out to be slug-like 

 animals, with shells either larger than their bodies, or 

 more or less capable of being concealed by the mantle : 

 they are all free, that is, they have the full power of 

 locomotion ; their shells have few, if any, voluties ; of 

 a thin and delicate substance in most, but rarely sculp- 

 tured ; never rough, and generally smooth and polished. 

 But what, perhaps, is the most remarkable feature 

 running through the majority, is the striking resemblance 

 they bear to tortoises, not merely in the oval depressed 

 form, and often coriaceous covering of their back, but 

 that this part should often be divided into angular or 

 hexagonal plates, precisely analogous to those reptiles. 

 Hence the expressive name of Chelisoma, given by 

 Mr. Broderip to the type which represents the Cyclo- 

 branchia, while the back of our Chelinotus seems as 

 if it was entirely covered with a shell divided into regular 

 series of hexagonal plates. Even the shells, if such 

 they may be called, of the typical Tectibranchia (as 

 Aplysidy &c.) resemble the thin horny layers on those 

 of tortoises ; while the Bulla, if they really belong to 

 the Cyprcea, so perfectly resemble these sea-slugs, that 



