AND EMBRYONIC FORMS. 423 



the whole length of the abdominal sack. Palpi small, transverse, suboval, not united 

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

 with rather large papillae. Anal opening small, with very small papillae. Super- 

 anal opening very large, colored on the inner edges and united below. Color of the 

 mass whitish. 



Columbus, Ohio, H. Moores. 



Unio Fabalis, Lea, = capillus, Say, = lapillus, Say. Trans. Amer. Phil. Soc, (2,) vol. iv. pi. 10, fig. 

 16, and Obs. vol. i. p. 96. 



Branchial uterus occupies the posterior part of the outer branchiae. Branchice small, 

 the inner ones the larger, curved below, free about half the length of the abdominal 

 sack. Palpi small, somewhat transverse, oval, not united on the posterior edges. 

 Mantle thin, dark-brown on the margin, inside and out, fringed below the branchial 

 opening, with maculations somewhat like Margaritana marginata. Branchial opening 

 rather large, with rather brown small papillae. Anal opening small, with numerous 

 small papillae. Super-anal opening rather large, dark-brown and maculate on the 

 outer edges, united below. Color of the mass whitish. 



Unio pressus, Lea. Trans. Amer. Phil. Soc, (2,) vol. iii. pi. 12, fig. 22, and Obs. vol. i. p. 64. 



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

 rounded below, free nearly the whole length of abdominal sack. Palpi small, sub- 

 angular, united half way down the posterior edges. Mantle thin, slightly thickened 

 on the margin. Branchial opening large, blackish on the edges and with numerous 

 papillae. Anal opening rather small, blackish and ivithout papilla). Super-anal open- 

 ing rather large, united for some distance below, blackish on the edges. Color of the 

 mass dirty white. 



Embryonic shell subtriangular, light-brown, has hooks. See Journ, Acad. Nat. Sci., 

 (2,) vol. iv. pi. 5, fig. 23 and Obs. vol. vi. p. 48. 



Cincinnati, Ohio, T. G. Lea ; Fox River, Illinois, H. C. Grosvenor ; and Columbus, 

 Ohio, H. Moores. 



Remarks. — This species is remarkable in its outward hard parts for its small lateral 

 teefh, and in the soft parts not having papillae on the edges of the anal opening. 



Unio coccinbus, Lea. Trans. Amer. Phil. Soc, (2,) vol. vi. pi. 5, fig. 12, and Obs. vol. ii. p. 12. 



Branchial uterus . No ova were found here, but the ovarium was filled with 



them. Branchial large, semicircular, inner ones much the larger, free nearly the 

 whole length of abdominal sack. Palpi small, subtriangular, united a short distance 

 on the posterior edges. Branchial opening rather large, with numerous colored papil- 

 lae. Anal opening rather large, with very small, colored papillae. Super-anal open- 

 ing large, colored within and united below. Color of the mass whitish. 



Fox River, Illinois, H. C. Grosvenor. 



