MALACOZOA. TROPIOPODA. LAMELLIBRANCHIATA. 241 



the anterior muscular impression large, and close to the 

 hinge anteriorly, the posterior larger. All the species 

 live in fresh water. 



GEXUS 1. ANODON. MUD-MUSSEL. 



Animal ovate or oblong, thick, with the mantle open 

 beneath and before, adherent, and having thickened, 

 often fringed, margins ; a posterior orifice for the anus, 

 and a short, incomplete, respiratory tube, of which the 

 mouth has two rows of tentacular papillae. Labial ap- 

 pendages triangular. Branchiae rather long, unequal. 

 Foot very large, thick, compressed, of a quadrangular 

 form. 



Shell ovate or oblong, generally thin, regular, equi- 

 valve, inequilateral, closed, umbones small convex and 

 with the dorsal slope more or less decorticated. Hinge 

 toothless, but presenting a lamina under the ligament, 

 which is external, and elongated. Muscular impres- 

 sions widely separated, very distinct. 



This genus differs little from Alasmodon, the animal 

 being nearly the same in both. The species reside in 

 lakes, pools, and rivers. 



1. Anodon anatinus. Duck Mud- Mussel. 



Shell ovate, inequilateral, moderately convex, with the an- 

 terior end short and rounded, the posterior truncato-angulate, 

 the umbones very small, the dorsal line nearly straight as far 

 as the ligament extends, then declinate to the upper posterior 

 angle ; the valves thin, brittle, semitransparent, concentrically 

 rugoso-striate, with conspicuous growth-lines, the epidermis 

 glossy, dull green, more or less tinged with dusky, and slightly 

 radiated ; the space about the hinge generally decorticated ; 

 the inside bluish-white, pearly in young, yellowish-white in 

 old shells. Length about four inches, height a third less. 



Found by Mr. Alexander Murray in the St. Fergus Canal, 

 and near Fraserburgh ; by Mr. Gray, near Peterhead. 



" Crows," says Pennant, "feed on these mussels, and also on 

 different shell-fish. It is diverting to observe, that when the 

 shell is too hard for their bills, they will fly with it to a great 

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