IG ANIMALS INHABITING BIVALVES. 



The second family is known by the English name of Cockle* : 

 these have the membrane called maiiteau or pallium divided 

 into two parts, being- open in front ; they project two separate 

 tubes from the upper end of the shell, which are commonly 

 very short ; from the front of the shell they protrude a fleshy 

 muscular foot, somewhat scythe-shaped ; they have two strong 

 muscles by which they open and shut their shells, one sitviated 

 near each end of the shell, the places of \\ Inch may be easily 

 perceived, as they almost always leave a distinct mark on the 

 interior surfaces. This family comprehends the Telliim, Car- 

 dium, Mactru, Donax, Venus, Area, and some species ofChama, 

 and a few Mhich, perhaps, are improperly placed with the 

 Solen. 



The third family are the Muscles ^f- : these ha\e the manteau 

 or pallium divided or open in front, like the last, but do not pro- 

 ject any tube beyond their shells ; they protrude a foot somewhat 

 tongue-shaped ; many species fix themselves hy abyss us or cluster 

 of threads; these have either three or four muscles for opening and 

 shutting their shells, two of which are generally larger than the 

 others, but they seldom leave any mark on the interior surface of 

 the shell. This family comprises the genera Pinna and Mytilus, 

 excepting a few improperly placed with the Mytili, as M.Frons, 

 Crista galli, &c. Here we may place the genus Unio of Ret- 

 zius and Lamarck, i. e. Mya Pictorum, &c. of Linnaeus. 



The fourth family are the Oysters : these are the Tethys of 



* See Adanson, pi. 18. f. Mofat. + Ibid. pi. 15. f. Lulat. 



