80 ON THE NAIADES, 



Anodonta Mortoniana. Plate XIII. fig. 37. 



Testa subelUptica, postice sub-bia7igulata, transve7'sd, vulde inxqidlalerali ; val- 

 vulis crassis ; epidermide perfused ; clivo umboniali sulcalo ; niargaritu argenteu 

 et iridescenti. 



Shell subelliptical, sub-biangular behind, transverse, very inequilateral ; valves 

 thick ; epidermis intensely brown ; umbonial slope furrowed ; nacre silvery and iri- 

 descent. 



Hab. River Parana, South America. Dr Burroiigh. 

 Cabinet of the Academy of Natural Sciences of Philadelphia. 

 Cabinet of Dr Burrough. 

 Diam. 1-2, Length 1-6, Breadth 3 inches. 



Shell subelliptical, sub-biangulate behind ; transverse, very inequi- 

 lateral, somewhat inflated, furrowed from the beak to the posterior 

 margin along the umbonial slope; substance of the shell thick; beaks 

 retuse and scarcely prominent; ligament long and narrow; epidermis 

 intensely brown and finely wrinkled ; anterior cicatrices distinct ; pos- 

 terior cicatrices confluent; dorsal cicatrices apparently none; cavity of 

 the beaks subangular and shallow ; nacre silvery white and iridescent. 



Remarks. — A single specimen of this species, which is distinct from 

 any described Aiiodonta I have seen, was sent to the Academy by Dr 

 Burrough. It is remarkably thick, silvery and iridescent, and has an 

 exceedingly dark epidermis. It most resembles, perhaps, the elon- 

 gaius of Swainson. It is less transverse than that shell, rounded only 

 anteriorly; it differs in not having "a strong flesh coloured tinge," and 

 is by no means so bright a brown as his beautiful figure. 



Named after S. G. Morton, M.D., corresponding secretary of the 

 Academy of Natural Sciences of Philadelphia. 



