192 ON THE NAIADES, 



Anodonta Mortoniana. Plate XIII. fiar. 37 



&• 



Testd subelliptica, postice sub-biangulafa, transversa, valde insequilalerali ; val- 

 vulis crassis ; epidennide perfused ; clivo umboniali sulcalo ; margariid argented 

 et iridescenti. 



Shell siibelliptical, sub-biangular be'iind, transverse, very inequilateral ; valves 

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

 descent. 



Hab. River Parana, South America. Dr Burrough. 

 Cabinet of the Academy of Natural Sciences of Philadelphia. 

 Cabinet of Dr Burrough. 

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



Shell subclliptical, 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 Anodonta 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- 

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

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

 is b}^ 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. 



