OF CONCHOLOGY. 157 



nent members. It differs from ca2-)S8eformis, in being more 

 iuflated and narrower, while its peculiar sac-development is 

 nearer the posterior basal edge in the female shell, and the 

 males of each are still more unlike in appearance. 



From Haysianus it differs by its longer form and thiner, 

 texture; and interriiptus, Eaf., which is the female of hrevidens, 

 Lea, is always broader, heavier and differently marked as to 

 coloration. 



Unio sacculus, Anthony. — t. 12, f. 3. 



Description. — Shell smooth, elliptical, inflated ; valves rather 

 thin; beaks somewhat prominent; epidermis olive-colored, 

 and nearly covered with fine green rays, which become 

 obsolete on the lower portion of the anterior half of the 

 shell; cardinal teeth small, compressed, erect, double in both 

 valves; lateral teeth short, curved and striated; nacre pearly 

 white and iridescent. 



Habitat. — Tennessee. 



My Cabinet. Cabinet of Hugh Cuming, London. Mus. 

 Comp. Zoology, Cambridge, Mass. 



Ohse'rvations. — Belongs to a group, the females of which 

 are characterized by a bulbous swelling, containing the egg- 

 sac. To this group belongs also, U. ca]}sseformis, Lea, 

 deviatus, Antli., fiorentinus, Lea, and many others. The 

 present species has this enlargement more globular than those 

 mentioned above, resembling in this respect the honey bag of 

 a monster bee. Some twenty or thirty specimens have at 

 various times been observed, all very uniform in appearance, 

 and no one who has ever seen it can well mistake it for any 

 other species. 



Alasmodon impressa, Anthony. — t. 12, f. 4. 



Description. — Shell smooth, elliptical, inequilateral, rounded 

 before and biangular behind; substance of the shell rather 

 thin; beaks subprominent, recurved, and undulate at tip; epi- 

 dermis greenish-yellow, relieved by darker, fine, green lines, 

 radiating from beak to basal margin, which is often emargi- 

 nate ; anterior portion of the shell regularly rounded, posterior 

 portion biangular and darker in color, often quite brown ; 

 marks of growth distant, and very conspicuous, only two or 

 three on each valve ; anterior cicatrices lightly impressed, con- 

 fluent; posterior cicatrices distinct and deeply impressed; 

 nacre silvery white and iridescent. 



Habitat. — Tennessee. 



My Cabinet. Mus. Comp. Zoology, Cambridge, Mass. 



