174 



UNIONID.E. 



U. ochraceus. 



and encloses a broad, depressed space, with the margins compressed 

 into a keel; base regularly rounded. Surface tolerably regular; 

 epidermis lying in fine loose folds about the posterior end, color 



olivaceous, rather yellowish 

 '*''■ JL_ in shells of the ordinary size, 



^^ - " and finely radiated and zoned 



--:-"T!^i-^ "^^ with dark olive over every 



part of the shell. Interior a 

 very delicate rose-color, or 

 deep salmon-color, tinted with 

 rose-red. Cardinal teeth com- 

 pressed, striated, directed for- 

 wards, and nearly parallel with 

 the hinge-margin ; lateral teeth 

 short ; cavity of the beaks capacious. Length, two and three fourths 

 inches ; height, two inches ; breadth, one and one fourth inches. 



Some specimens are found mucli larger. I have one from Penn- 

 sylvania which measures four inches, two and two fifths inches, 

 one and three fourths inches. Such shells become quite thick and 

 proportionally elongated posteriorly ; they lose the radiations of the 

 epidermis, which is of a dark olive-color. I do not know tluit any 

 such sliclls have been found in Massachusetts. 



This shell is very rare, and I do not know of its having been 

 found anywhere except in Plymouth ponds. AVhcn young it is 

 scarcely to be distinguished from U. cariosus ; but it is more in- 

 flated, and the radiations of the epidermis are finer, and cover more 

 of the shell ; nor is it so glossy, and its interior is more colored. 



Ocniis MARGARITANA, ScnuMAcnER. 1817. 



Shell transverse, inequilateral ; hinge like that of Unio, except 

 that it is destitute of a lateral tooth. 



Margaritana arcuata. 



Fig. 75. 



Shell more or less kidne3^-sliaped, very inequilateral, thick, beaks not promi- 

 nent; epidermis pitchy-black; within bluish-Avhite ; teeth erect, conical, grooved. 



Akmnodouta nratata, Barnes, Silliman's Jonrn. vi. 277, pi. 12, fi.c. 20 (1823). — Adams, 

 Shells of Vermont, in Thomps. Hist. 165. — Gould, Inv. Mass 1st cd. 113, tig. 75. 

 — Dk Kay, Nat. Hist. New York, 197, pi. 14, fig 224. 



