UNIO UNDULATUS. 



SPECIFIC CHARACTER. 



Transversely undulated ; umbo literate. 



SYNONYM. 



Unio UNDULATUS. Bctmcs. Silliman's Jovrnal^ vol. vi. 

 p. 120, pi. 2. 



description. 



Transversely oval, somewhat oblong, with large, distinct 

 undulations, three or four in number, directed towards the 

 anterior margin and not proceeding directly from the um- 

 bo : surface with a few abbreviated, longitudinal lines, pla- 

 ced without any regularity : umbo placed far backward, 

 not prominent, hardly elevated above the general curva- 

 ture, more or less literate w^ith short, irregular lines or 

 slight elevations : hinge margin compressed, nearly recti- 

 linear, prominently angulated or subalated at tip, in the 

 more perfect specimens with numerous, connected, regu- 

 lar lines, curved to the edge and undulating it : anterior 

 margin rectilinear from the extremity of the hinge mar- 

 gin to the rounded inferior half, and undulated by the tip 

 of the grooves of the disk : posterior margin very short, 

 regularly rounded : base very obtusely rounded, in many 

 specimens a little contracted near the anterior termina- 

 tion : fosset elongated, very distinct : within bluish-white ; 

 perlaceous. 



PLATE XVI. 



