28 NEW UNIONIDiE, MELANID^, ETC.. 



pressed ; dorsal cicatrices very small and placed near the centre of the cavity of the 

 beaks; cavity of the disk deep and wide; cavity of the beaks very shallow and 

 rounded ; nacre bluish white and iridescent. 



Soft Paris. — JBrancJdce large, much rounded below, the inner ones much the larger, 

 free nearly the whole length of the abdominal sack. Pal2n moderately large, sub- 

 triangular, not united on the posterior edges. Mantle very thin, with a small margin. 

 Branchial opening large, with numerous small, brown papillae. Anal opening small, 

 with very small brown papilla3. Super-anal opening small and united some distance 

 below ; color of the mass dirty white. 



Remarlcs. — Four specimens of this species were sent to me among others from the 

 collection of the Smithsonian. I recognized it at once to be different in outline from 

 any I had seen from the rivers of the Middle States, and I am surprised that it should 

 not have been observed before. We might very naturally suspect that it would be 

 likely to be an aberration oi fluviatilis=cataracta, Say, but its oblong form, submedial 

 beaks, carina and callous margin at once forbid its being confounded with that species. 

 In the callous margin it reminds one o^ implicata Say, ^ Neiotonensis (nobis), but that 

 species is more transversely oblique and more biangular posteriorly, and usually of a 

 darker epidermis. In outline it is nearest to BenecUctH (nobis), but the carina is not, 

 like that species, elevated into a wing, nor has the Benedictii a callous margin. In 

 the undulations of the tips of the beaks it is allied to implicata, ha\'ing no double 

 curve or granulations like fiuviatilis and Benedictii. In the specimens before me two 

 are green with obscure rays, two are yellowish olive without rays. All have one or 

 two rather broad, brown marks of growth. The inflation is great about the middle of 

 the disk, and there is a disposition to flattening about the medial portion which 

 causes, at the basal margin, a slight emargination. I name this after H. C. Williams, 

 who sent these specimens to the Smithsonian, and I am permitted, by the liberality of 

 the Secretary, to retain two specimens as types in my cabinet. 



Anodonta Trtonii. pi. 10, fig. 27. 



Testa Isevi, obliqua-elliptica, subcompressa, sublenticulari, valde insaquilaterali, postice subbiangulari, 

 antice rotundata; valvulis tenuibus ; natibus prominulis, subcompressis, ad apices undulatis ; 

 epidermide fulgida, vel virente vel fuscescente, obsolete radiata; margarita cseruleo-alba at valde 

 iridescente. 



Shell smooth, obliquely elliptical, rather compressed, sublenticular, very inequi- 

 lateral, subbiangular behind, rounded before ; valves thin ; beaks a little prominent, 

 somewhat compressed, undulate at the tips; epidermis shining, green or dull brown, 

 obscurely radiate ; nacre bluish white and very iridescent. 

 Proc. Acad. Nat. Sci., 1862, p. 169. 



Hah. — Schuylkill River above Philadelphia, Delaware Eiver at League Island. 



