3« NEW UNIONID.*; OF THE 



diverging from the Jjeaks to the margin. In all the three specimens before me, the 

 nacre in the thickened parts and in the teeth has a slight tint of gamboge yellow. 



Unto RtTTERSViLLENSis. PI. 60, fig. 181. 



Testa laevi, transverse elliptica, subinflata, valde inaequilatetali, postice obtuse angulata ; valvulis subtenuibus, 

 antice paulisper crassioribus ; natibus prominulis, ad apices regulariter et elegaatissime undulatis; epider- 

 mide vel fusca vel luteo-fusca et vald^ radiata; dentibus cardinalibus parvis, compressis, acuminafs, 

 crenulatis, in utroque valvulo duplioibus ; lateralibus longis, lamellatis subcurvisque ; margarita caeruleo- 

 alba et valde : 



Shell smooth, transversely elliptical, somewhat inflated, very inequilateral, ob- 

 tusely angular behind; valves rather thin, a little thicker before; beaks a little 

 prominent, regularly and beautifully undulate at the tips ; epidermis brown or yel- 

 lowish brown, and very much rayed; cardinal teeth small, compressed, pointed, crenu- 

 late and double in both valves ; lateral teeth long, lamellar and slightly curved ; nacre 

 bluish white and very iridescent. 



Proc. Acad. Nat. Sci. 1859, p. 155. 



Hah. — Rutersville, Fayette County, Texas. Prof. C. G. Forshey. 



My cabinet and cabinet of Prof. Forshey. 

 Diam. -8, Length 13, Breadth 24 inches. 



Shell smooth, transversely elliptical, somewhat inflated, very inequilateral, ob- 

 tusely angular behind ; substance of the shell rather thin, a little thicker before, beaks 

 a little prominent, regularly and beautifully undulate at the tips, the undulations 

 being close and parallel, and forming an angle on the middle of the beaks ; ligament 

 rather long, somewhat brown ; epidermis shining, disposed to be brown towards the 

 beaks and yellow towards the margins, with numerous rays especially on the pos- 

 terior portion and with distant lines of growth ; umbonial slope in the male slightly raised 

 and obtusely angular, in the female very much enlarged and,_rounded ; posterior slope 

 slightly raised, striate, somewhat wrinkled, with one well marked ray on each valve 

 from beak to margin ; cardinal teeth small, compressed, pointed, crenulate and double 

 in both valves; lateral teeth long, lamellar and slightly curved; anterior cicatrices 

 distinct and well impressed; posterior cicatrices confluent andvery slightly impressed ; 

 dorsal cicatrices placed across the centre of the cavity of the beaks ; cavitjfof the shell 

 rather deejj and wide ; cavity of the beaks rather shallow and subangular ; nacre 

 bluish white and very iridescent. 



Remarks. — I owe to the kindness of Prof. Forshey a number of this species, but they 

 were generally much broken on their arrival. The one figured is a nearly perfect 

 adult female ; the largest is three inches wide. The undulations are remarkably 

 small, regular and parallel ; and on the anterior slope they curve from the margin round 

 to the middle of the beak; here they form an angle, by suddenly taking (for a short 



