NEW FRESH WATER AND MARINE SHELLS. 277 



This species is most nearly related to U. costatus, (Raf.) but differs in being far 

 more ventricose, and has very prominent umbones, which are just the reverse in the 

 costatus. The diameter through the umbonial slope is profound. 



U. NODiFERUS. PI. 38, figs. 4, 8. — Obtusely subovate, ventricose, moderately thick ; surface with a few 

 nodules about the middle of the valves, and smaller ones near the ligament margin ; a slight, not very 

 wide, furrow extends from beak to base ; posterior margin approaching to a regular curve ; beaks 

 eroded ; within white ; cardinal teeth robust, prominent, direct, and profoundly sulcated in old shells ; 

 epidermis chestnut-brown. 



Proceed. Acad. Nat. Sc.,Vol. i., p. 19, 1841. 



Approaches U. prasinus, but differs in being proportionally longer, more convex; 

 in having a brown epidermis, narrower anterior side, and oblique posterior mar- 

 gin. 



U. PLECTOPHORUS.* PI. 38, fig. 7. — Trapezoidal, thick ; valves flattened on the sides, slightly contracted, 

 marked with irregular arched, obtuse, interrupted folds, extending from the beaks nearly to the base ; 

 umbonal slope angular ; posterior slope plicated ; beaks not prominent, profoundly eroded ; ligament 

 margin elevated j posterior extremity truncated obliquely inwards ; basal margin contracted ; epidermis 

 nearly black ; within white, with a pui'ple margin ; cardinal teeth direct, very thick, sulcated ; lateral 

 teeth slightly arched. 



U. AiiATUs. Proceed. Acad. Nat. Sc, Vol. iv., p. 154. 



U. PLECTOPHORUS. " " " " " p. 162. 



Inhabits Flint River, Georgia. 



Allied to V. Sloatianus and U. trapezoides, Lea. 



U. MississippiENsts. PI. 38, fig. 11. — Narrow-elliptical, ventricose, slightly contracted from beak to base ; 



hinge margin parallel with the base ; posterior margin very oblique, concave ; extremity somewhat 



pointed, angulated; beaks with angular ridges; epidermis polished, olivaceous, with numerous 



dark green rays ; within highly perlaceous ; cardinal teeth prominent, oblique, double in each valve. 



Found by Dr. Dickeson in one of the tributaries of the lower Mississippi. Allied 



to U. Naslwillianus, Lea., but is proportionally longer, with finer undulations on the 



beaks, and the rays extend over the whole disk. 



MELANIA. 



M. suBLiRATA. PI. 38, fig. 1.— Elongate-conoidal ; volutions six, the sides flattened above ; whorls of the 

 spire with a carinated angle near the base of each, and longitudinally ribbed ; ribs not prominent; 

 upper whorls with two distant revolving lines on each ; base of the body whorl striated, the upper 

 portion of body whorl obscurely ribbed ; color olivaceous with obscure brown bands. 



Inhabits Savannah River. 



* In the Proceedings of the Academy this name is erroneously printed plecircfhorus. 



