OF THE FAMILY OF NAIADES. 427 



2. Unto Rubiginosus. Plate VIII. fig. 10. 



Testa in(Bquilaterali, transversa, postice suh-hiangulari, antice rotun- 

 datd : valvulis sub-crassis ; natibus prominentibits, recurvis, postice sub- 

 angulatis ; dente cai'dinali magna, laterali crasso ; margarita salmonis 

 colore. 



Shell inequilateral, transverse, sub-biangular behind and rounded be- 

 fore; valves somewhat thick; beaks prominent, recurved, sub-angulated 

 behind; cardinal tooth large; lateral tooth thick; nacre salmon co- 

 loured. 



Hab. Ohio. 



My Cabinet. 



Cabinet of T. G. Lea. 



Cabinet of Prof. Vanuxem. 



Cabinet of the Academy of Natural Sciences. 



Diam. 1-2, Length 2-1, Breadth 2-6 inches. 



Shell somewhat ventricose ; substance of the shell some- 

 what thick ; umbones slightly elevated ; beaks recurved, sel- 

 dom decorticated, almost touching, whitish, possessing several 

 concentric undulations, which are lost along the umbonial 

 slope, which is carinate ; a small curved elevated line passes 

 from the point of the beaks to the margin above the posterior 

 margin ; ligament rather large passing from the points of the 

 beaks ; dorsal margin oblique ; posterior dorsal margin cari- 

 nate and slightly emarginate ; posterior margin angular : pos- 

 terior basal margin very slightly curved ; basal, anterior and 

 anterior dorsal and basal margins rounded ; epidermis colour 

 of rust, sometimes salmon yellow, slightly wrinkled and show- 

 ing the marks of growth ; rays in young specimens percepti- 

 ble; cardinal tooth sulcate, broad and not elevated, often 

 single in both valves; the tooth in the left valve closing in a 

 cavity w^hich sinks almost into the cavity of the beaks of the 

 right valve ; lateral teeth rather thick, elevated, straight, ge- 

 nerally double in both valves ; in the left valve the upper 

 division is less elevated and shorter; anterior and posterior 

 cicatrices both distinct ; the smaller posterior cicatrix is situ- 



VOL. III. — 5 Q 



