UNITED STATES AND ARCTIC AMERICA 



Hob. — Medina River, Texas, A. L. Ileermann, M. D. 



My cabinet and cabinets of Academy of Natural Sciences and Dr. Heermann. 

 Diam. -S, Length 1-6, Breadth 2-5 inches. 



Shell winged, smooth, elliptical, compressed, very inequilateral, obtusely biangular 

 behind, round before ; substance of the shell rather thin, irregularly thickened be- 

 fore ; beaks a little prominent, scarcely undulate at the tips ; ligament rather short 

 and light brown ; epidermis yellowish brown', light towards the beaks, shining, with- 

 out rays, with well marked distant lines of growth ; umbonial slope slightly raised 

 and rounded ; posterior slope raised into a wing, with two obscurely impressed lines 

 from the tips to the margin on each valve ; cardinal teeth small, somewhat conical, 

 crenulate and double in both valves ; lateral teeth long, lamellar and nearly straight : 

 anterior cicatrices distinct, moderately impressed and rather large ; posterior cicatrices 

 confluent, large and very slightly impressed; dorsal cicatrices in a row above the 

 centre of the cavity of the beaks ; cavity of the shell shallow and wide ; cavity of 

 the beaks not deep, obtusely angular ; nacre pale salmon and purplish, and exceed- 

 ingly iridescent on the posterior half of the disk. 



Remarks. — Several specimens were brought by Dr. Heermann, three of which I 

 have before me, all of different ages. It is not easily confounded with any other 

 species, and is more nearly allied to alatiis, Say, than any other of our North Ame- 

 rican species. It is, however, by no means so high in the wing, is of a different outline, 

 and a very much smaller species. In outline it is nearest to generosus, Gould, but 

 it is not of so regular an ellipse, approaching, indeed, to oblongation. In the cardinal 

 teeth they are totally different, those of generosus being long and lamellar, and being- 

 single in the left valve. In the youngest specimen the ligament is concealed, in 

 the older ones it is apparent. The nacre of Heermannii is very remarkable. It is 

 beautifully iridescent, and a purple hue generally pervades the disk, the cavity of the 

 beaks taking on a salmon tint. The thickening portion of the cavity is irregular, 

 but in each there is a ridge running obliquely from the cavity of the beaks to the 

 basal margin, stronger in the oldest than in the youngest specimen. The undulations 

 of the tips are so minute as scarcely to be observed. The lines of growth are well 

 marked and distant. I name this after our fellow-member, Dr. Heermann, who has 

 for many years been actively collecting and adding many valuable specimens in 

 various branches of natural history to the collection of our Academy. 



Unio aureus. PI. 26, fig. 264. 



Testa kevi, subtriangulari, compressa, ad latere paulisper planulata. subimequilatcrali ; valvulis sub- 

 crassis, antice crassioribus ; natibus subelevatis, ad apices aeuminatis ; epidermide aurea. striata. 

 obsolete radiata; dentibus cardinalibus crassis, erectis, striatis, iu utroque valvulo duplicibus ; 

 lateralibus eurtis et obliquisj margarita alba et irideseente. 



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