314 MEMOIRS OF THE CARNEGIE MUSEUM. 



Gabb, 1861 (Delaware River, Tacony, Philadelphia Co., and Bristol, Bucks Co.) 

 Bruckhart, 1869 (Lancaster Co.) 



Hartman & Alichener, 1874 (Schuylkill, Delaware, and Susquehanna Rivers). 

 Pilsbry, 1894 (York Furnace, York Co.) 

 Scliick, 1895 (Delaware River, Philadelphia). 

 Ortmann, 19096, p. 204. 



Caffrey, 1911, reports U. ochraceus from the Delaware in Northampton County, but there is no question 

 that under this name he designates U. cariosus. 



Characters of the shell: Of medium size, rather thin when young, but becoming 

 thicker when old. Outhne ovate or subelliptical, rather short and high, but old 

 males are often somewhat elongated, and may be slightly over one-and-a-half 

 times as long as high; but generally the length is less than this. Anterior margin 

 rounded. Lower margin more or less curved. Upper margin short, straight or a 

 little convex, passing into a blunt angle or gradually into the obliquely descending 

 posterior margin. Posterior end a rounded, blimt angle. Beaks moderately 

 swollen, not much elevated, anterior to the middle of the shell. Beak-sculpture 

 (Marshall, 1890, fig. 8) consisting of about five not very distinct bars, the first 

 subconcentric, the following ones slightly double-looped, with a light sinus in the 

 middle, obsolete in the last bars. Upon the posterior slope, the bars are effaced. 

 Valves regularly convex, somewhat flattened upon the sides. Posterior ridge very 

 indistinct, practically absent. Posterior slope gently convex, or almost flat. 



Epidermis j'^ellow, very smooth and shining. The yellow is wax- or straw- 

 yellow, with hardly a trace of green in it, but sometimes inclining to brown or 

 reddish brown. Rays either entirely absent, or present upon the posterior slope 

 and a little in front of it. They are variable in width, but are generally fine, 

 straight, and sharply defined, dark green or blackish in color, contrasting strongly 

 with the light epidermis. Concentric bands of light or dark color absent or in- 

 distinct. In old specimens the color of the epidermis is less bright, and becomes 

 dirty grayish or brownish yellow. 



Hinge well-developed. Pseudocardinals generally two in each valve, quite 

 variable in shape. In young specimens they are rather compressed, in older ones 

 more stumpy and ragged. Interdentum practically absent. Laterals lamellar, 

 generally somewhat elevated and truncate at their posterior ends. Beak-cavity 

 moderate. Dorsal muscle-scars in the beak-cavity. Anterior adductor-scars 

 distinct and impressed, posterior ones less distinct. Nacre silvery white, often 

 suffused with cream- or salmon-color, but not reddish. 



later (1900, p. 529, footnote 1, and p. 530, footnote 2) says, that the two figures had been accidentally 

 transposed. But these figures are copies from Hartman & Michener (1874, figs. 183, 184) where the 

 same mistake is made. I think, both of these figures represent cariosus, and the one named ochraceus 

 is certainly the female of cariosus. 



