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ART. IV. — New Unionidce of the United States. 

 By Isaac Lea, LL. D. 



In my last paper, which the Academy did me the favor to publish in its late 

 volume, I treated chiefly of new exotic Unionidce from Siam. The soft parts of which 

 unfortunately were not preserved, and therefore I had not the opportunity of making 

 any examination of them. In the present paper, which treats of forty-one new indi- 

 genous species, I have had the advantage of examining the soft parts of very numer- 

 ous specimens from various parts of the United States, many of which were living, 

 the remainder being preserved in alcohol. Careful diagnoses have been made of the 

 soft parts in all cases where I had the advantage of possessing them ; and owing to 

 the continued exertions of many kind friends, in various parts of the Union, whose 

 names will be found in connection with the diagnosis of each of the species, I have 

 been enabled to give full attention to the soft parts of nearly all the new species in 

 this paper. I have descriptions of the soft parts prepared, of about one hundred and 

 sixty more, including most of the indigenous species known, as well as many new 

 ones. These will follow in the series of communications to the Academy. 



It will be observed in the descriptions herein of Unio rubellinus, that I have referred 

 to the fact that some species have a byssus at mature age. I have treated this sub- 

 ject more at large in the Proceedings of the Academy, Sept. 1856. In February. 1857, 

 I made a communication also to the Academy on a discovery I had made that some 

 of the Unionidce, at least, had visual organs, and were sensitive to light.* This very 

 important fact has not been further entered into by me since, except to observe several 

 other species to be sensitive to light, viz.: U. cylindricus, Say, U. ?°ubiginosus, (nobis,) 

 and Anodonta imbecilis, Say. I hope my friend Dr. Leidy will take up this branch of 

 the subject, and give us the anatomy of this minute eye with other portions of the 

 economy of these interesting Mollusca. 



Unio Abbevillensis. PI. 6, fig. 34. 



Testa laevi, oblonga, subioflata, ad lateris planulatis, valdc iosequelaterali, postice biangulata ; valvulis 

 crassis ; natibus proniinulis ; epidermide brunnea, striata; dentibus cardiualibus wagnis, crassis, in 

 utroque valvule- duplicibus; lateralibus prselongis, lamellatis subcurvisque; niargarita vel alba vel salrno- 

 nis colore tincta.. 



Shell smooth, oblong, rather inflated, flattened on the sides, very inequilateral, bi- 

 angular behind, valves thick ; beaks a little prominent ; epidermis brown, striate ; car- 



* Prof. Halderaan, T afterwards found. (Monog. No. 6) had observed the retraction of "the protruded 

 branchial canal of "Unio radiatus," when light was intercepted. 



