82 THE HISTORY OF ANIMALS. [u. IV. 



internal flesh, for some of them have no flesh at all, as the 

 echinus ; in others it is entirely internal and out of sight, 

 except the head, as the land snails and those called coccalia, 1 

 and in the sea the purpura 2 and the ceryx, 3 the cochlus, and 

 all the turbinated shells. 



2. Of the rest some are bivalves, others univalves. I call 

 those bivalves which are enclosed in two shells ; the univalves 

 are enclosed in one shell, and the fleshy part is uncovered, 

 as the, lepas. 4 Some of the bivalves can open, as the 

 pectens and mya, for all these are joined on one side, and 

 separated on the other, so as to shut and open. There 

 are other bivalves which are joined on both sides, as the 

 solen ; others which are entirely enclosed in their shells, and 

 have no external naked flesh, as those which are called tethya. 5 



3. And there is a great difference amongst the shells 

 themselves, for some are smooth, as the solen, mya, and 

 some conchas, called by some persons galaces ; 6 other shells 

 are rough, as the limnostrea, 7 pinnae, some kinds of conchae, 

 and the whelk ; and of these some are marked with ridges, as 

 the pecten and a kind of concha, others are without ridges, as 

 the pinna and another species of concha. They also differ in 

 thickness and thinness, both in the whole shell and in certain 

 parts of the shell, as about the edges, for in some the edges 

 are thin, as the mya; others are thick-edged, as the limnostrea. 



4. Some of them are capable of motion, as the pecten, for 

 some persons say that the pectens can fly, for that they 

 sometimes leap out of the instrument by which they are 

 taken. Others, as the pinna, cannot move from the point 

 of attachment ; all the turbinated shells can move and crawl ; 

 the lepas (patella) also feeds by going from place to place. 

 It is common to all those with hard shells to have them 

 smooth in the inside. 



5. Both in univalves and bivalves the fleshy part is united 

 to the shell, so that it can only be separated by force ; it is 

 more easily separated from the turbinated shells ; it is a 

 characteristic of all these shells, that the base of the shell 

 has the helix directed from the head. All of them from their 

 birth have an operculum ; all the turbinated testacea are 



1 Some small land snail with a conical shell. 



2 Purpura. 3 Whelk. 4 Patella, limpet. 

 5 Ascidians. 6 Chama, L. 7 Ostrea edulis. 



