UNIO NEXUS. 



DESCRIPTION. 



Shell transversely triangular-subrhomboidal, murh in* 

 /lated, thick : bmks prominent: anlcrior side much de- 

 pressed, in its middle elevated so as to make an almost rec- 

 tilinear hinge margin, Avith a broad, shallow groove, which 

 extends from the beak to the anterior margin : anterior 

 margin forming nearly a right angle with the base, ob- 

 tusely emarginate in the middle by the termination of the 

 groove : umbonial slope carinated, in consequence of the 

 depression of the anterior side : limiile very short : poste- 

 rior margin very short, rounded : colour light brownish, 

 obsoletely radiated : within white : cardinal teeth direct 

 lateral teeth rectilinear, short, with but little obliquity 

 posterior accessory cicatrix ob]i<|ueIy elongated, slender 

 anterior accessory cicatrix coniluent. 



SYNONYMS. 



Unio nexus, Nob.^ Transijljania Journal, vol. 4, p. 



627, 18J1. 



U. ARCiEFORMis, Trails. Jlmcr. Philos. Soc. vol. 4, N. 

 S. 1832. 



PI, 51. 



