AND EMBRYONIC FORMS. . 417 



latter had not the uterus "pervading the four leaves of the branchiae as the former 

 has. This multiplied uterus also exists in U. mulliplicatus* and Kleinianus. The 

 ovisacks of rubiginosus are long and slender, and when extruded by the parent they 

 are rose red, the eggs giving a color to the whole ovisack. The eggs were only so 

 far advanced as to present the vitellus granulated, and this was bright red, surrounded 

 by white liquor amnii. We therefore have four species with the uterus pervading 

 the four leaves of the branchiae, — viz. : 



Unio multiplicatus, 



Unio rubiginosus, 



Unio Kleinianus, 



Unio subrotundus . 

 And three species with the remarkable character of red eggs, — viz. : 



Unio rubiginosus, 



Unio subrotundus. 



Unio JEsopus. 

 The first two being included in the list of the four branchiae being occupied by the 

 uterus. See remarks on subrotundus. 



Unio undulatus, Bar. Amer. Jour. Sci., vol. vi. p. 120. 



Branchial uterus occupies the whole of the outer branchiae. Branchice. rather large, 

 semicirculai', inner ones very much the larger, free the whole length of abdominal 

 sack. Palpi large, oval, thin, united half way down the posterior edges. Mantle 

 rather thin, thickened at the edges. Branchial opening large, with numerous 

 brownish papillae. Anal opening large, with numerous, very small, pale papillae. 

 Super-anal opening very large, with a linear black edge, not united below. Color 

 of the mass whitish. 



Embryonic shell triangular, brown or white, has no hooks. See Jour. Acad. Nat. 

 Sci., vol. iv. pi. 5, fig. 22, and Obs. vol. vi. p. 48. 



Columbus, Ohio, H. Moores. 



Remarks. — I have never .before observed in the embryonic shells a difference in 

 those of the same parent. In the only female I have received of this species, with 

 the embryonic shells matured, some were clear white, while others were dark-brown. 



Unio ("jibbosus, Bar. Amer. Jour. Sci., vol. vi. p. 262. 



Branchial uterus occupies the whole width of the outer branchiae. Branchice very 

 wide, curved below, inner one much the larger, free more than half the length of 

 the abdominal sack. Palpi very small, subtriangular, free the whole length of the 

 posterior edges. Mantle thin, thickened on the margin. Branchial opening large, 



* See Journ. Acad. Nat. Sci., vol. iv. pi. 30, fig. 105, and Obs. vol. vii. p. 40. Also Proc. Acad. Nat. Sci., 

 December 6th. 1859. 



10U 



