106 MONOMYAIRA. 



striated transversely. Three-fourths of an inch long. Inhabits 

 the Mediterranean. 



CLASS IL— CONCHIFERA. 



Animals soft with articulations, destitute of head or organs 

 of vision, and always fixed within a bivalve shell ; having exter- 

 nal branchiae ; a simple circulation, and a unilocular heart. 



All the shells of this class live in the sea or in fresh water. 

 None of the animals have an internal shell. The body is inva- 

 riably soft, and the mouth is situated near the left side of the 

 hinge. 



Lamarck divides this class into the two following orders : — 

 I. MoNOMYAiRA, with One muscle of attachment ; shell exhibit- 

 ing interiorly but one subcentral muscular impression. — II. Di- 

 MYAiRA, having at least two muscles of attachment ; the shell 

 exhibiting interiorly, two separate, lateral, muscular impressions. 



ORDER I.— MONOMYAIRA. 



The animal provided with one muscle of attachment, leaving 

 a nearly central muscular impression. 



Section I.— Without a ligament, or unknown ; or in its stead 

 a tendinous chord, which connects the valves. 



TRIBE I. BRACHIOPODA. 



Provided with two opposite, elongated, ciliated arms, situ- 

 ated near the mouth, which are rolled up spirally when the 

 animal is at rest ; mantle having two separate lobes in front, 

 which envelope the body. — Shell bivalve, adhering to extrane- 

 ous marine bodies, either by the shell itself being in contact 

 with them, or attached by a tendinous chord. The shells are 

 not quite equivalve, and open by a hinge. 



