EXOTIC UNIONID.B. 83 



distant. In this specimen there are some wrinkles on the posterior slope, but this 

 may not be a permanent character. The lateral teeth are remarkable for their 

 length and for being single in the left and double in the right valve. It has the 

 character of costa> or raised rays diverging from the tip of the beaks, which is so 

 general with the species of South America, and which has not yet been observed in 

 any North American, nor in any European, African or Asiatic species. In outline it 

 is nearest to U. Paranensis, (nobis), but cannot l)e confounded with that species, 

 being thinner in the substance of the valves, being much more inflated and in having 

 a higher wing and broader posterior slope. It is nearer in outline to Diplodon (Unio) 

 rotunchim, Spix, than any other described in his fluviatile shells of Brazil, but it is 

 quite different in the teeth, and in being more rounded and more vcntricose. 



Unio Caldwellii. PI. 43, fig. 145. 



Testa sulcata, elliptica, subinflatii, postic^ obtuse angulata, inaequilaterali ; valvulis subcrassis ; natibus 

 subelevatis, ad apices minute undulatis ; epidermide luteo-fusca eradiataque ; dentibus cardinalibua 

 compressis, elevatis crenulatisque ; lateralibus sublongis subrectisque ; margarita salraonis colore tincta 

 et irideseente. 



Shell sulcate, elliptical, somewhat inflated, obtusely angular behind, inequilateral ; 

 valves rather thick ; beaks rather raised and minutely undulate at the tips ; epidermis 

 yellowish brown and without rays ; cardinal teeth compressed, elevated and crenu- 

 late ; lateral teeth rather long and nearly straight ; nacre salmon color and iridescent. 



Unio CaMvrlfn, Lea. Proe. Acad. Nat. Sci., 1858, p. 118. 



Eab.—lsthmns of Darien. H. C. Caldwell, M. D., U. S. Navy. 



My cabinet. 

 Diam. -8, Length 1-5, Breadth 2-3 inches. 



Shell sulcate, elliptical, somewhat inflated, obtusely angular behind and rounded 

 before, inequilateral ; substance of the shell rather thick ; beaks rather raised and 

 minutely undulate at the tips; ligament rather short, somewhat thick and light 

 brown ; epidermis yellowish brown, with distant marks of growth and without rays ; 

 umbonial slope slightly raised and rounded ; posterior slope rather narrow, with an 

 impressed line from the beaks to the posterior margin ; cardinal teeth rather large, 

 compressed, elevated and crenulate ; lateral teeth rather long, nearly straight and 

 terminating in an arched plate; anterior cicatrices distinct and well impressed; 

 posterior cicatrices confluent and moderately impressed ; dorsal cicatrices situated 

 above the centre of the cavity of the beaks ; cavity of the shell moderately deep and 

 wide; cavity of the beaks rather deep and subangular; nacre salmon color and 

 iridescent. 



Remarks.— A single specimen was In-ought by Dr. Caldwell from his perilous expedi- 

 tion on the Isthmus of Darien with Lieut. Strain, and these molluscs formed part of the 

 food on which the party subsisted. It is somewhat like omfus, (nobis), but is much 



