MYTILUS. 



Lithodomns: from Anodon and Avicula, together with ha.- 

 marc^i' s 3feleagrma, it is obviously so distinct that we need 

 not enter upon its particular marks of discrimination; and 

 one character will suffice to distinguish it from Modiola 

 and JLithodomuSy namely, the pointed terminal umbones of 

 Mytilus. 



The true Mytili, so named, as we liave been in- 

 formed, from their resemblance in shape to a Mouse, 

 are marine;* they are very abundant on almost every 

 rocky coast, being found attached by their coarse 

 filamentous byssus to whatever substance first comes 

 in their way. We do not think that after being once 

 attached, they habitually disengage themselves, though 

 it appears to us probable that when disengaged by the 

 force of the sea, they may live for some time without 

 being in any manner affixed: there appear to be many 

 species, which are mostly smooth on the outside and 

 covered with a strong horny epidermis, which is generally 

 worn off about the umbones; several are, however, more or 

 less deeply and longitudinally grooved : a few very small 

 teeth are occasionally observable close to the umbones 

 within, and there is sometimes a small septum placed 

 just within the beak in each valve, to v/hich the anterior 

 adductor muscle is in those species attached. 



The British species of this Genus enumerated by 

 Turton are four : we are far from being satisfied that they 

 are distinct, for the principal character upon which Turton 

 seems to place dependance is the number of minute teeth 

 within the anterior point. 



The fossil species with which we are acquainted are 

 not numerous, they occur, however, in some of the beds 

 below the chalk, (as well as in most of those above it,) 

 but particularly in the crag. 



In our plate we have represented 



Fig. 1 & 2. Mytilus achatinus^ Latn. 



3. crenatus, Lam. 



4. polymorphus, Gmel. 



* We have here said '* the true Mytilit hecaiise it may become necessai'y to 

 separate from them some shells which accord very well with them in form, but 

 which, nevertheless, differ from them in some of the characters of the animal, 

 :uid iii being inhabitants of river waters : such as the Mytilus pohjmorphusy Gmel. 

 found in the Danube; and in the Commercial Docks, near London, &c. 



