456 UNIONID^S, THEIR SOET PARTS 



thicker on the border. Branchial opening small, salmon color, interspersed with 

 black and having a few rather small papillae. Anal opening small, salmon colored, 

 intei-spersed with black and having slightly crenulated edges. Super-anal opening 

 rather large, slightly united below. Color of the mass whitish, and inclining to 

 salmon. 



Potomac, at Fort Washington, Prof. Baird. 



Remarks. — In the Trans. Amer. Phil. Soc, 1836, vol. vi. pi. 15, fig. 44, I made 

 some observations on the soft parts of the Unionidai and gave a drawing of the 

 branchial uterus of this species. 



Unio Fisiierianus, Lea. Trans. Amer. Phil. Soc, (2) vol. vi. and Qbs. vol. ii. p. 8, pi. 4, fig. 8. 



Branchial uterus occupies nearly the whole length of the outer branchiae. Bran- 

 chice very long and narrow, the inner ones somewhat the larger, free nearly the 

 whole length of abdominal sack. Palpi very large, nearly elliptical, united only at 

 the upper posterior edges. Mantle very thin, thickened at the edges, nearly black 

 along the posterior edges. Branchial opening rather large, with numerous very 

 small, light colored papillae. Super-anal opening long, united for some distance be- 

 low. Color of the mass whitish, inclining to salmon color. 



Canal, near the Chain Bridge, District of Columbia:, Prof. Baird. 



Remarks. — I have had the advantage of examining quite a number of specimens 

 kindly sent to me in a living state by Prof. Baird, of the Smithsonian Institution. 

 The color of the nacre of all the specimens were purple, except one, which was 

 white, with a tint of salmon in the cavity of the beaks. In the character of the 

 branchiae being free nearly the whole length of the abdominal sack, it is very dif- 

 ferent from nasutus, Say, to which it is so nearly allied in the exterior or hard parts. 

 In that species the branchiae are only free at the posterior point of the foot, and Prof. 

 Agassiz is quite mistaken in assigning nasutus as well as Msherianus to the genus 

 Eurynea, proposed by Mr. Rafinesque and adopted and amended by the Professor, 

 which the latter describes as having " the gills united the whole length of the foot " / / 

 Fisherianus is free nearly the whole length of the foot or abdominal sack, while Prof. 

 Agassiz quotes it among the division proposed, under the name of Eurynea ! See 

 " Archiv fur Naturgeschchite," 1852, and " Shells of New England," by Wm. 

 Stimpson. 1851. 



