ANODQN. 



beings; and seeing that^ as characters of generic im- 

 portance^ so little dependance can be placed upon the 

 teeth, it might suggest the propriety of uniting under 

 one generic appellation all Lamarck's Naiades^ dividing 

 the Genus so formed into several sections by the charac- 

 ters of the hinge; for we find a considerable degree of 

 accordance in the general characters of all: we do not 

 venture to take such a step, because the state of our 

 knowledge is not yet sufficient to enable us to complete 

 the subject in the manner we could wish. 



The Anodontes, then, as distinguished from other 

 genera, are equivalve, inequilateral, transverse bivalves, 

 generally very thin, but in a few instances thick, always 

 covered with a more or less dark coloured green or oliva- 

 ceous epidermis ; their hinge line is mostly pretty straight, 

 and their ligament, which is external, is generally elon- 

 gated. Hinge without teeth. Muscular impressions two, 

 of which the posterior is compound; muscular impression 

 of the mantle entire, seldom distinct. In their young state 

 the Anodontes are most commonly very flat and thin shells, 

 increasing, however, in thickness and convexity with 

 age ; this circumstance joined to that of their great varia- 

 bility in general form, depending in a certain degree on 

 their situation, renders the species very difficult to distin- 

 guish, and appears to have been the reason that numerous 

 varieties of the common English Horse Muscle have been 

 by some authors considered as so many distinct species. 

 A learned friend of ours, who has taken the pains to 

 collect a great number of series from various localities, 

 has thus proved their identity. Notwithstanding this 

 fact, we have reason to believe that the recent species 

 inhabiting foreign climates are numerous; but we do not 

 know of any fossil species, except we are justified in con- 

 sidering the bivalve from the Coal Measures, figured in 

 Sowerby's British Mineralogy," tab. 386, under the 

 name of Mytilus crassus, as an Anodon; which, upon 

 examination of specimens, we are unable to demonstrate, 

 but we find strong reason for believing that it may prove 

 so. 



Fig. 1 Anodon alatus, which we have thus named on account of its wing; in 

 which it resembles the Unio alatus. 

 2, Anodon anatinus. 



