AND EMBRYONIC FORMS. 411 



Unio acutissimus, Lea. Trans. Amer. Phil. Soc, vol. iv. pi. 10, fig. 18. Obs. vol. i. p. 99. 



Branchial uterus occupies the whole width of the outer branchise, like that of 

 penicellatus. Branchial wide, slightly curved below, inner ones much the larger, 

 free nearly the whole length of abdominal sack. Palpi very small, suboval, not 

 united on the posterior edges. Mantle thin, thickened on the margin, colored on 

 the posterior basal inner edge. Branchial opening small, protruded, with small, 

 brown papilla. Anal opening large, with very minute brownish papillse. Svsper- 

 anal opening large, slightly united below. Color of the mass whitish. 



Embryonic shell elongate pouch-shape, white, near to that of pencillatus, has no 

 hooks. See Journ. Acad. Nat. Sci., vol. iv. pi. 5, fig. 5 and Obs. vol. vi. p. 47. 

 Etowah River, Georgia, Bishop Elliott. 



Bemar7cs —In one of the five specimens before me there is a fine filamentous byssus 

 about an inch long, thicker than a horse hair, flattened and semitransparent, without 

 the appearance of fibre, but rather horn-like. The point of attachment is in the pos- 

 terior base of the foot, which is there a little enlarged and rounded, presenting the rudi- 

 ments or remains of a second byssus. The outer end of the filament, in this specimen, 

 where it was attached to the foreign substance to which the animal had anchored 

 itself, is evidently perfect, showing the true length of the byssus. At this outer 

 end it is divided into four filaments each evidently having been fastened to 

 the foreign substance. While but one of these five specimens has the bijssits re- 

 maining, it is evident, from the cicatrix or impressed cut, that all have been endowed 

 with it, and that it is characteristic of this species and Gonradianus to be anchored, 

 and, where they are not found so, a rupture has taken place and thus given them 

 the power of locomotion. That young Uniones of some, if not all the species, are 

 anchored by a byssus was long since discovered by Dr. Kirtland, but it has never 

 before, I believe, been observed in adults. (See more extended remarks on this 

 subject in Proceed. Acad. Nat. Sci., Sept., 1856.) 



Unio strigosus, Lea. Trans. Amer. Phil. Soc, vol. viii. pi. 9, fig. 9. Obs. vol. iii. p. 36. 



Branchial uterus — — . No ova were found here, but the ovarium was full. 

 Branchiw very wide, curved below and oblique posteriorly, inner ones much the 

 larger, free nearly the whole length of abdominal sack. Palpi small, suboval, not 

 united on the posterior edges. Mantle thin, thickened at the margin. Branchial 

 opening small, with small, brownish papillse. Anal opening large, with numerous 

 small papilla?. Super-anal opening small, brownish on the inner edges, united 

 below. Color of the mass whitish. 



Columbus, Georgia, Bishop Elliott. 



Unio radiatus, Lam. An. sans Vert., vol. vi. p. 73. 

 Branchial uterus occupies the posterior portion of the outer branchiw and extend? 



