1278 DIPLODON 



Unio quadratis Lea, Pr. Ac. N. Sci. Phila., YV , 1859, p. 306; 



Jl. Ac. N. Sci. Phila., TV, i860, p. 360, pi. lxi, fig. 185; 



Obs., VIII, i860, p. 42. pi. LXI, fig. 185. 

 Margaron (Unio) qinufraris T^ka, Syn., 1870, p. 36. 

 Diplodon qnadrans Simpson, Syn., iqoo, p. 885. 



This shell, w^hich is in the Wheatley collection, is supposed 

 to have come from Texas. Nothing like it has been reported 

 by any one else from that state and there seems to be nothing 

 from the Texan or Mexican region that is in any way related 

 to it. The umbonal region is so eroded that no traces of beak 

 sculpture remain, but the character of the teeth, the general 

 appearance, color and sculpture seem to ally it to the forms of 

 South America. The greatest degree of inflation is well for- 

 Avard and from this it is rather regularly wedge-shaped in 

 front and behind. 



Subgenus Cyci/jmya Simpson, 1900. 



Cyclomya Simpson, Syn., 1900, p. 886. 



Shell obovate to suborbicular, narrowed in front, produced 

 just behind the center of the base, generally slightly pointed 

 about the middle of the posterior end, with a scarcely percep- 

 tible posterior ridge and a slight dorsal wing behind ; beaks 

 high, irregularly radial ; hinge line strongly arched, curved 

 behind and incurved in front of the beaks ; the lower pseudo- 

 cardinal in the right valve largest, often much split up into 

 denticles, those of the left valve variable, generally dentilate ; 

 two lower anterior scars deep, united, the upper very deep, 

 separate. 



Animal having the gills rather short, inner the longer, 

 united throughout to the abdominal sac, outer subangular be- 

 low ; palpi large, projecting behind; branchial opening large, 

 with a few stout papill.ne ; anal opening separated from the 

 branchial by a bridge, but not separated from the superanaL 

 opening. 



Type, Unio fnnehralis Lea. 



