AND EMBRYONIC FORMS. 421 



The posterior adductor muscle is enormously large, exhibiting great power in closing 

 the valves. 



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

 Nat. Sci., vol. iv. pi. 5, fig. 19, and Obs. vol. vi. p. 48. 



Columbus, Ohio, H. Moores. 



Remarks. — This well-known and well-characterized species is remarkable for its 

 outward form, and particularly in the enlargement of the female on the posterior 

 basal margin and umbonial slope. The fleshy enlargement of the flap is hard. The 

 absence of papillae on the anal opening is very remarkable in a Uhio. 



Unio cylinpricus, Say. Nich. Ency., Amor, ed., Art. Conch., pi. 4, fig. 3. 



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



filled with dark saffron-yellow ova, which were well developed. Branchial very- 

 wide, the lower margin nearly parallel with the upper margin, inner ones rather 

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

 transverse, subelliptical, angular at the posterior end, united half way down the pos- 

 terior edges. Mantle rather thick, much thicker on . the margin, saffron-yellow, 

 deeper on the margin, the outer edge of which is blackish. Branchial opening rather 

 large, with numerous small papillae, covered with pigmentum nigrum. Anal opening 

 very large, tvithout papilla}, but with slightly crenulate edges, inside edges black, 

 outside edges yellowish. Super-anal opening very large, dark-brown on the edges, 

 covered with pigmentum nigrum within, slightly united below. Color of the mass 

 saffron, deeper in the larger muscles and foot, which is covered with pigmentum 

 nigrum. On the inner side of the mantle, along the junction with the branchiae, 

 the veins leading to the branchiae are beautifully displayed, the interspaces being 

 covered with pigmentum nigrum. 



Columbus, Ohio, H. Moores. 



Remarks, — The remarkable outline of the valves of this species would lead one to 

 expect some essential difference in the form of the soft parts, but there does not ap- 

 pear to be any very remarkable difference. The color is unusually saffron, and the 

 absence of papillae on the anal opening is remarkable, as well as the pigmentum 

 nigrum. It is to be regretted that none of the specimens had developed embryonic 

 shells. It is possible that when observed they may be found to differ from any 

 species yet described. 



Unio striatulus, Lea. Jour. Acad. Nat. Sci., (2,) vol. v. p. 55, and Obs. vol. viii. p. 59. 



Branchial uterus . No ova were found here, but minute ones were in the 



ovarium. Branchiae large, thin, nearly semicircular, free two-thirds the length of 

 abdominal sack. Palpi rather large, thin, subtriangnlar, united nearty half way 



107 



