UNIONID.E. 289 



These animals live sunk perpendicularly in the 

 mud of rivers, with the front end downwards, and the 

 siphonal edge even with the surface of the mud, but 

 sinking themselves deeper when disturbed ; they are 

 also found under the shelter of stones in rivers and 

 running water, with stony banks. 



The family contains three genera, — 



1. Anodon. Hinge toothless. 



2. Alasmodon. Hinge with short anterior teeth. 



3. Unio. Hinge with short anterior and long pos- 

 terior teeth. 



]. Anodon Lam. (Fresh- Water Muscle.) 



Shell oblong, thin, rather compressed behind ; hinge 

 margin toothless. 



122. J. Anodon cygneus. Swan Fresh- Water Mus- 

 cle, (t. 1. f. 8.) Shell oval, tumid, rounder and 

 ventricose in front, compressed and more or less 

 angular above behind, covered with an olive pe- 

 riostraca. 



Mytilus cygneus. Linn.; Montagu, T. B. 170. 



Anodonta cygnea. Drap. ; Lam. 



Anodon cygneus. Turton, Biv., Man. ed. 1. 17. 



Young. The hinder slope more compressed and 

 dilated. 



Var. 1. cellensis. Shell large, ovate-oblong, very 

 ventricose, thin, brittle, rather produced be- 

 hind, upper and lower edge nearly parallel, 

 straight. 



Mytilus cellensis. Schroet, Flussc. t. 2. f. 1. 



Anodonta sulcata. Lam. Hist. v. 85. ; Pfeiffer, i. 

 110. t. 6. f. 1., ii. 6.; Nilson, 113. 

 o 



