78 NEW UMONIU.E OF THE UNITED STATES. 



comprcssis, in utroque valvule duplicibus; lateralibus brevibus, percraasis corrugatisque ; inargarlta ar- 

 gentea et valdo iridesoeDtP. 



Shell smooth, subrotund, thick, sublenticular, equilateral; valves thick, thicker 

 before ; beaks elevated, swollen ; epidermis dark brown, with obscure rays ; cardinal 

 teeth thick, erect, compressed, double in both valves ; lateral teeth short, very thick 

 and corrugate ; nacre silvery white and very iridescent. 

 Proc. Acad. Nat. Sci. 1860, p. 307. 



Hab. — Coosa River, Wetumpka, Alabama. E. R. Showalter, M. D. 



My cabinet and cabinets of Dr. Showalter, Dr. Hartman and Mr. Anthony. 

 Diam. -8, Length 1-1, Breadth 1-2 inch. 



Shell smooth, nearly round, thick, somewhat lenticular, equilateral ; substance of the 

 shell thick, thicker before ; beaks elevated, swollen ; ligament very short and light 

 brown ; epidermis dark brown, inclining to bottle green, with obscure broad rays on the 

 middle, with very distant marks of growth, shining on the umbones and striate to- 

 wards the margin ; umbonial slope slightly raised and obtusely angular ; posterior slope 

 flattened, with an impressed line, and in some specimens two yellow lines in each valve 

 from the beaks to the posterior margin ; cardinal teeth thick, erect, compressed, double 

 in both valves ; lateral teeth short, very thick and corrugate ; anterior cicatrices rather 

 small, distinct and well impressed ; posterior cicatrices distinct, small and well im- 

 pressed ; dorsal cicatrices placed above the centre of the cavity of the beaks ; cavity 

 of the shell shallow and rounded ; cavity of the beaks very shallow and obtusely 

 angular; nacre silvery white and very iridescent. 



Soft parts. — Branchial uterus not charged, but ova were found in the ovarium. 

 BranchioB rather large, thin, semicircular, inner one much the larger, free more than 

 half the length of abdominal sack. Palpi small, suboval, united above at the posterior 

 edges. Mantle thin, thickened at the border, and margined with a black line. 

 Branchial opening rather large, with numerous small, dark papillge. Anal opening 

 large, with numerous small, nearly black papillae on the inner edges. Super-anal open- 

 ing large, bordered with black and not united below. Color of the mass dirty white. 



Remarks. — This little species is nearly allied to circulus, (nobis), and reminds one 

 also of ebenus, (nobis). The beaks are higher than in the former, and not recurved, 

 as in the latter. It has the black border of the latter. The epidermis is very dark 

 brown, and some specimens are inclined to deep green and to be yellowish on the pos- 

 terior slope. In the diagnosis in the Proceedings of the Academy of Natural Sciences, 

 it was stated to be without rays ; better specimens since received show that the dark 

 green hue of the disks is caused by broad indistinct rays. There is a disposition to 

 depression before the umbonial slope, which makes a slight emargination on the ante- 

 rior basal margin. The largest of four specimens before is about 1^x1^ inch. The 

 lateral teeth are very thick and short and disposed to be double in the right valve, 



