UNIO CLAVA. 



Plate III.— Fig. 1. 



DESCRIPTION. 



Shell cuneiform, very oblique; posterior side pro- 

 duced, compressed, with an oblique furrow rapidly 

 widening from the umbo; ligament margin arcuate, 

 very oblique; umbo elevated, narrowed, inclining for- 

 wards; beaks curved to a point, terminal; epidermis 

 wrinkled, olive-yellow or brownish, with interrupted 

 rays over the umbo, disappearing with age; within 

 white, very iridescent posteriorly; cardinal tooth in 

 the left valve nearly parallel with the ligament mar- 

 gin. 



SYNONYMES. 



U. clava, Lam. An. sans vert. vol. vi. p. 74. 



U. scalenius, Raf. Ann. gen. des Sc. Phys. vol. v. p. 43. pi. 



lxxxi. fig. 24, 25. Poulson's trans, p. 47. 

 U. modioliformis, Say. 

 Cab. A. N. S. No. 1117. 



OBSERVATIONS. 



A beautiful species when perfect, and common in 

 the western rivers. With age the posterior side be- 

 comes greatly produced and compressed, and gene- 

 rally furnished with irregular indentations. Allied to 

 U. oviformis, nob. and decisus, Lea. 



B 



