Martini's figure of U. Pictorum resem bles this shell in outline. Vol. 6.
Very common in the Delaware and Schuylkill rivers.
Gmelin, Ed. Syst. Nat. p. 3220, refers to Lister's figure as a variety of Olga Radiata, a native of Malabar : but we have ventured to consider it a distinct species ; the largest we have seen was brought from Wilkesbarre by Mr. Lard. Vanuxem, in length 21, breadth, 31 inches. The animal is rarely infested by a. parasite. See the article Hydrachne, 6. U. Ochraceus. Shell thin, fragile, translucent, subuvate, hinge margin 4ornewhat rectilinear, colour from a pale reddish orange to a pale olive ; generally radiate with dull green and with minute wrinkled radii ; anterior margin very finely wrinkled ; beaks decorticated ane approximate, with two or three smal concentric undulations ; within bluish white or ochraceous, tinged with rec near the base ; teeth very oblique any much compressed.
Length, one inch and a quarter breadth, one and three quarters.
Plate 2. fig. 8.
This shell, in many respects, resew bles the preceding, with which it is found but is not so obtuse in front, and is much less rounded at the hinge margin, it is al so much thinner, and the beaks approach each other more closely.
7. U. Named:8. Shell thin, oblong compressed, rostrated, horn colour o fuscous, with fine cronded wrinkles, ob scurely radiate with green ; within blu ish white ; beak cavity hardly any, teeth crenate.
Length, one inch and one eighth breadth, two and three-fifths.
Very common in the Delaware an Schuylkill.
Plate 4. fig. 1.
fuscus, augusiior, exalters pal to Cuneatim protensus. Lister. Conch. tad 151. fig. 6.
8. U. Jilates. Shell moderately thicl sub-triorgular, generally gaping at th posterior part of the base, fuscous, writ kled ; beaks not prominent, placed vet far back and decorticated ; base alma rectilinear ; hinge margin remarkably ob lique, rising near the terminatidn of the cartilage into an alated projection, and forming almost a right angle with the in ferior slope, which is nearly equal in length ; within red-purple, often with nu merous tubercles, which, upon the gaping limb, are confluent ; cicatrices very rough ; teeth crenate, the external lami nated one obsolete, only one in each valve being very perceptible.
Length, including the projection, three inches and four-fifths ; breadth, five inch es and a half.
Plate 4. fig. 2.
EnCyC. 3frth. vol. 63, tab. 248, fig. 1. a. b? Lesueur found this species in Lake Erie, very thin and fragile.
The specimen from which this descrip tion is taken, and also the next species, were purchased by ..111i'.-Joseph Watson, at the sale of the late Professor Bar ton's collection, and by him presented to the Academy of Natural Sciences of Philadelphia. There is also a specimen in the Museum of Mr. Peale.
9. U. C'ylindricus. Shell very thick, sub-cylindrical, emarginate before, pale horn-colour varied with greenish ; hinge margin undulated obliquely across the wrinkles, rough on each side, rectiline ar and parallel to the base ; beaks broad and prominent, with a deeply impressed posterior lunule ; within perlaceous, teeth thick and crenate ; cavity of the beaks very deep.
Length, one inch and three-tenths ; breadth, three inches and one fifth.
Plate 4. fig. 3.
From the collection of the late profes sor Barton; it is said to be found in the river Wabash.