288 NEW UNIONID^, MELANIDiE, ETC., 



confluent, large and very sliglitly impressed; dorsal cicatrices placed across the 

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

 and wide ; nacre whitish. 



Remarks. — I am indebeted to Prof. Henry, Secretary of the Smithsonian Institu- 

 tion, for the advantage of seeing and describing this shell, which is the first that has 

 been received from the great river Youkan, of the new territory Alaska, recently 

 acquired from Kussia in Arctic America. It is greatly to be regretted that other 

 species of the Unionidce have not been found, as they no doubt exist where these 

 were found. I have several specimens before me, all of uniform character. 



In outline this species is near to Anodonia ovata (nobis), but it is more inequi- 

 valve and more inflated, of a darker color in the epidermis and has closer marks of 

 growth. All the specimens received were dead and much injured. I am not aware 

 by whom they were taken and brought here. 



Anodonta Geanadensis.* pi. 41, fig. 100. 



Testa Isevi, elliptica, subinflata, inmquivalva, insequilaterali, postice obtuse angulata, antice rotunda ; 

 valvulis subtenuibus ; natibus prominulis ; epidermide ve) lutea vel virido-radiata ; margarita 

 c£eruleo-alba et valde iridescente. 



Shell smooth, elliptical, somewhat inflated, inequivalve, inequilateral, obtusely 



*"In the 'Proceedings of the Acad, of Nat. Sci.,' April, 1856, I described a new species of Triqueta 

 (Hyria, Lam.), which I called lanceolata. It was made from a single valve in a collectiou from China. In 

 the diagnosis made in the 'Proceedings' it was not mentioned that this valve was somewhat twisted, being 

 fearful that the curved condition arose from accidental circumstances, and not from a normal condition like 

 Area tortuosa, Jjin. Subsequently, in the 'Journal of the Academy,' vol. iii, and in 'Observations on the 

 Genus Unio,' vol. vi, I published a full account of this peculiarly interesting species, having received perfect 

 specimens, one of which was well figured. In this paper I thought that, as the original name of lanceolata, 

 made from a single imperfect valve, did not apply to the perfect shell, science would be subserved by a de- 

 scriptive name. I proposed to call it contorta, and redescribed it under that name with full remarks and 

 observations. At that time it was the only member of the family Unionidce which was known not to be 

 equivalve. Subsequently, in describing a species of Spatha under the name of Natalensis, I mentioned that 

 it was 'slightly inequivalve.' 'Journal Acad. Nat. Sci.,' vol. vi, and in 'Observations on the Genus Unio,' 

 vol. xi. 



" In 1865 I published in the ' Proceedings of the Academy ' the diagnosis of a new Unio from China, which 

 is inequivalve and twisted. This I named tortuosus. The full description and figure, with remarks, is in a 

 paper which I have prepared for the Journal of the Academy. These constitute all the inequivalve species of 

 the family which I have seen until recently. 



"The collection made by the late Mr. Thomas Bridges, botanist, who, during his travels in Central America, 

 visited Lake Nicaragua, has been kindly placed in my possession, part by Col. E. Jewett, and part by Mr. W. 

 M. Gabb, Palaeontologist of the California Geological Survey. Very much to my surprise and satisfaction I 

 found that several species of Unio and Anodonia had this inequivalve character. 



" It may be here remarked that there seems to be a predisposition, in the Unionidce of Central America, to 

 this very unusual character in the Umonidce, while in IVlesico, United States and Canada, where so many 

 species have beee described, there has not been a single one obse^ed. These observations and the follow- 



