UNITED STATES. 81 



Hah. — Flint River at Lanier, Georgia, Dr. II. M. Nei.slcr; at Macon, Georgia, J. 

 C. Plant. 



My cabinet and cabinets of Ur. Neisler, Dr. Lewis and Mr. Plant. 

 Diam. 1-4, Length 2-2, Breadth 2-7 inche.*. 



Shell regularly and numerously plicate, (the fold.s being nearly parallel,) quadrate, 

 much inflated, flattened at the sides, very inequilateral; substance of the shell thick, 

 thicker behind; beaks prominent and thick; ligament rather long, somewhat thick 

 and dark brown ; epidermis nearly black, brownish towards the basal margin ; 

 umbonial slope very much raised and rounded ; posterior slope raised into a carina, 

 very wide and filled with numerous, slightly curved folds ; cardinal teeth very large, 

 thick, crenulate and double in both valves ; lateral teeth thick, rather long, minutely 

 granulate and curved ; anterior cicatrices distinct, large and very rugose ; posterior 

 cicatrices confluent, large and slightly impressed ; dorsal cicatrices situated on the 

 under side and near the edge of the ^^late, wdiich is very large ; cavity of the shell 

 very deep and rounded ; cavity of the beaks very deep and angular; nacre pure white 

 and very iridescent. 



Soft imrts. — Branchial litems not charged, but one of the four specimens had the 

 appearance of ova in the ovarium. Brancliku very large, semicircular, inner one much 

 the larger, free two-thirds the length of the abdominal sack. Palpi large, rather 

 pendant, suboval, united nearly half way down the posterior edges. Mantle thin, 

 whitish. Branchial oj^ening very large, with numerous, rather small, brownish papilla?. 

 Anal opening very large, with numerous, very small brownish papilla?. Super-anal 

 opening very long, colored within and slightly united below. Color of the mass dirty 

 wdiite. 



Remarhs. — This is among the most remarkable of the plicate group. It is the only 

 species I know where the folds are nearly parallel with the basal line and run nearly 

 parallel with each other ; this parallelism is continued over the umbonial slojie to the 

 basal margin, so that when this margin is held towards the eye they are seen to be 

 strikingly straight. The folds are stronger towards the basal margin, and being 

 parallel to it, cause an overwrapping of one of the valves at the base in cases where 

 the individual has not quite arrived at maturity. In the mature specimens the basal 

 edges of the valves are equal. The folds being alternate, could not be formed but hy 

 alternate overwrapping at the incremental margin. It is greatly to be regretted that 

 we have no specimen with perfect beaks, nor a young one. It is evident that the 

 folds on the beaks must be very small, and lose that regularity which pervades the 

 whole disk, except at the margin of the anterior portion, where all trace of folding is 

 lost. In some of the specimens there is a disposition in the epidermis near the basal 

 margin to be of a lighter brown, while the upper portion is black or blackish. The 

 interior border beyond the nacre is disposed to be reddish brown. 



