412 UNIONISE, THEIR SOFT PARTS 



below the inferior border. The ovisacks are very large, subovate, blackish below 

 and in one of the specimens there were eighteen on each side.* Branchice very 

 large, rounded below, inner ones the larger, blackish on the lower edges, united the 

 whole length of abdominal sack. Palpi very large, sub triangular, attached about 

 half way down the posterior edges. Mantle rather thin, very much thickened and 

 dark on the posterior and basal margins, a coarse fringe extending below the bran- 

 chial opening.f Branchial opening large, with numerous closely-set, dark-brown 

 papillae, on the ends of which the eyes are very perceptible, they being very sensi- 

 tive in this species. Anal opening rather small, usually with very minute, brown 

 papillae, but in some specimens these papillae are replaced by a mere corrugated 

 edge. Super-anal opening "not very large, united below. Color of the mass 

 whitish. 



Embryonic sliell ovately pouch-shape, white, some specimens had imperfect hooks 

 at the base. See Journ. Acad. Nat. Sci., vol. iv. pi. 5, fig. 20. Obs. vol. vi. p. 48. 



Mohawk, N. York, James Lewis, M. D. 



Unio complanattjs == Mya complanata, Soland, MSS. in British Museum and Dillwyn's Des. Cat. 



Branchial uterus —r-. No ova were found here, but an immense number were 

 found in the ovarium. Branchice very large, curved below, inner ones much the 

 larger, free nearly the whole length of abdominal sack. Palpi rather large, sub- 

 triangular, united nearly half way down the posterior edges. Mantle thick, thicker at 

 the margin. Branchial opening rather large, with numerous dark-brown papillae. 

 Anal opening large, with numerous, very small, dark-brown papillae. Super-anal 

 opening large, not united below, with a dark line on the exterior edges. Color of 

 the mass whitish. 



Schuylkill River, near Philadelphia; Schuyler's Lake, N. York, J. Lewis, M. D.; 

 and Potomac River at Fort Washington, Prof. S. F. Baird. 



Remarks.— I examined about one hundred living specimens from the Potomac on 

 the 19th May, and observed but one with the branchial uterus charged, having 

 segmented ova, while the females of radiatus from the same place were all fully 

 charged with developed, pouch-shaped young. Thus the period of the two species 

 seems to be very different. 



* I have observed, in November and December, that the young of radiatus are extruded in ovate sacks, 

 perfectly white, 9-20ths by 4-20ths by l-20th, containing about 1200. The young are complete, the valves 

 usually lying open. January 31st, 1857, a fine, large saek was thrown out. February 2d, another. February 

 11th, two. February 13th, two. February 17th, two. March 2d, two. March 5th, two. Observations were 

 not carried further. Subsequently, May 19th, 1863, I found many with full charged branchial uterus. 



t In these specimens, from Mohawk, N. Y., there is a striking difference from those described by me from 

 the Schuylkill. See Trans. Amer. Phil. Soc, vol. vi. pi. 15. Obs., vol. i. p. 52. The papilla? of the fringe 

 are numerous and very close, obtuse, matted and speckled, and terminate below by a sudden enlargement, 

 edged by larger papillae. 



