mutelidjE. 505 



The species of Mycetopus inhabit the rivers of South 

 America. The shells somewhat resemble those of Anodonta, 

 but the valves are sub-equilateral, and gape at the sides. 



Species of Mycetopus. 



siliquosus, D'Orb. ventricosus, D'Orb. 



soleniformis, D'Orb. 



Fain. MUTELIDjE. 



Mouth and lips small; labial palps very large, oval, 

 attached by their straight edges, without any free points as 

 in Unionidce. Mantle-lobes united posteriorly, and pro- 

 longed into two short, unequal, siphonal tubes ; gills 

 large, nearly equal, united to the body. Foot, large, thick, 

 compressed, tongue- shaped, angular in front. 



Shell equivalve, oblong, covered with a hard, polished 

 epidermis ; beaks small, turned to one side, and nearly 

 straight. Hinge large, linear, toothless, tubercular or cre- 

 nate ; ligament external, marginal. Muscular impressions 

 two, separate, lateral. 



Fluviatile. 



Genus MUTELA, Scopoli. 



Outer gill united to the mantle as far as its extremity ; 

 inner gill entirely united to the foot. 



Shell equivalve, inequilateral, transverse, pearly within ; 

 beaks small, recurved, nearly straight. Hinge long, linear, 

 attenuated towards the middle, tuberculose along its length; 

 ligament external, marginal. Pallial impression simple. 



Syn. Mutel, Adans. Scapha, Humph., not Gray. 



