42 ON THE NAIADES, 



Diam 2-4, Length 2-5, Breadth 3'5 inches. 



Shell very globose, inequilateral, translucent, very smooth and 

 bright ; connate before and behind the beaks ; substance of the shell 

 rather thin ; beaks very round, incurved ; epidermis very smooth, and 

 pale yellow or straw colour; umbones very round; cardinal teeth 

 very lamellar, elevated, double in the right valve, and very crenate and 

 single in the left ; the line of the lateral and cardinal teeth form two 

 curves; anterior cicatrices distinct; posterior cicatrices confluent; 

 dorsal cicatrices situated in the cavity of the beaks on the under side 

 of the cardinal teeth ; palleal cicatrix deeply impressed ; cavity of 

 the beaks very round and very deep ; nacre thicker near the margin, 

 beautifully pearly white and iridescent. 



Remarks. — We owe to Col. Long and Mr T. Peale the knowledge 

 of this singular and distinct species. Without a tubercle and almost 

 ray less, for those on the posterior slope are obsolete, it is among the 

 most beautiful and interesting species known. The Academy is in 

 possession of four fine specimens, making a complete suite of different 

 ages. Three of them are perfect enough to display the character of 

 this genus, Symphynotci, notwithstanding their great globosity. It 

 is more capacious than any of the Naiades I have seen, and the light 

 yellow or straw coloured epidermis is very peculiar — in form it most 

 resembles, perhaps, the Unio occidens (nobis), but it has no rays. In 

 the younger individuals there is a transverse rib-like appearance which 

 I have noticed in no other species of the family. 



Symphynota Woodiana. Plate V. fig. 13 



J3* 



Testa subpentagonu, postice angulaid, super umbones turgidu, insequilaterali, 

 transversa; valvulis tenuibus ; epidermide tenebroso-fuscd et obscuro-radiatd ; 

 natibus U7idulatis ; margarilu alba et iridescente. 



Shell subpentagonal, angular behind, turgid over the umbones, inequilateral, trans- 

 verse ; valves thin ; epidermis dark brown and obscurely rayed ; beaks undulated ; 

 nacre pearly white and iridescent. 



