AND EMBRYONIC FORMS. 433 



Unio retusus, Lam. An. sans Vert., vol. vi. p. 72. 



Branchial uterus occupies the posterior part of the outer branchiae, having about 

 twenty-five ovisacks on each side protruding beyond the lower edge of the branchiae, 

 and are altogether like those of cariosus. Branchial rather small, thin, rounded 

 below, united the whole length of the abdominal sack. Palpi small, subtriangular, 

 united only a short distance down the posterior edges. Mantle very thin, with a 

 broad margin, thickened and colored on the edges. Branchial opening rather large, 

 with small brownish papillae. Anal opening very small, with very minute crenu- 

 lations on the inner edges. Super-anal opening large, united slightly below. Color 

 of the mass dilute salmon. 



Embryonic shell elongately pouch-shape, clear white, has no hooks. Journ. Acad. 

 Nat. Sci. (2), vol. iv. pl.,5, fig. 7. Obs. vol. vi. p. 47. 



Cincinnati, Ohio, T. G. Lea and J. Clark. 



Remarks. — In 1838 I received from my brother a dried specimen of a female 

 with the ovisacks fully charged. More recently I received four specimens in alcohol 

 from Mr. Clark. All these proved to have no papillae on the edges of the anal 

 opening, but they were crenulate. 



Unio pyramid atus. Trans. Am. Phil. Soc. (2), vol. iv. pi. 16, fig. 39, and Obs. vol. i. p. 119. 



Branchial uterus . No ova were found here, but they were in the ovarium. 



Branchial large, nearly semicircular, inner ones much the larger; in the female 

 before me, the lower edges are irregular and very minutely crenulate, free nearly 

 the whole length of the abdominal sack. Palpi rather large, thin, subtriangular, 

 united one-third down the posterior edges. Mantle very thin, with a broad margin, 

 slightly thickened on the edges. Branchial opening rather large, with numerous 

 small, brownish papillae. Anal opening large, brown on the edges, with numerous 

 small papillae. Super-anal opening rather large, dark on the edges and slightly 

 united below. Color of the mass dirty white. 



Cincinnati, Ohio, J. Clark. 



Remarks. — -The living specimens which I had for observation, I found to be unusu- 

 ally sensitive to light. 



Unio irroratus, Lea. Trans. Amer. Phil. Soc. (2), vol. iii. pi. 5, fig. 5. Obs. vol. i. p. 11. 



Branchial uterus occupies a small portion of the posterior part of the outer bran- 

 chiae, in seven or eight pendant ovisacks on each side, these ovisacks being volutes of 

 different lengths, but the embryos were not sufficiently developed to indicate the form 

 of the embryonic shell. Branchial rather large, very oblique, rounded below, inner 

 one much the larger, free about half the length of the abdominal sack. Palpi rather 

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



110 



