176 UNIONID^. 



Mr. Lea regards our shell as identical with the European Mija 

 margaritifera of the older authors, the Unio clong-ata of Lamarck, 

 &c. ; but the shells which I have had an opportunity of examining 

 present some constant differences. The foreign shell is shorter, the 

 beaks more nearly central, and more elevated, and the portion of 

 the interior, within the pallial impression, is minutely granulated ; 

 and as my foreign specimens agree accurately with the figures of 

 Chemnitz and Turton, I am induced to think there may ho a con- 

 stant difference. The intervention of an ocean would strengthen 

 the supposition. I have, therefore, felt disposed to retain the very 

 ajjpropriate name of Barnes, until more fully satisfied. The Euro- 

 |)ean shell is the famous river pearl-mussel, in which pearls of con- 

 siderable beauty are occasionally found. But, as far as I have ob- 

 served, they are not oftener found in our Alasmodon than in other 

 species of fresh-water mussels. 



Margaritana iindulata. 



Fig. 76. 



Shell transversely-ovate, inequilateral, angular behind; beaks tumid, elevated, 

 undulated ; epidermis dark-green, obscurely rayed ; one cardinal tooth in each 

 valve, supported hj a strong internal rib. 



Unlo uiuhtlatus, Say, Nicholson's Encyc. (Anicr. cd.) iv. pi. 3, fig. 3 (1816). — Bixxey's 

 reprint, 53, pi. 71, fig. 3. 



Alasmodonta iindulata, Barnes, Sillimau's Journ. vi. 279 (1823). — Adams, Shells of Ver- 

 mont, in Tliom])S. Hist. 165. 



Mya Iindulata, Wood, Suppl. pi. 1, fig. 5. 



ilargaritana undidata. Lea, Trans. Amcr. Phil. Soc. (new scries) vi. 13.'j ; Synops. Naiad. 

 44 ; 3d ed. 42. 



Vnio hians, Valexc. Recueil d'Ohs de Zool. par Ilumb. ct Bonpl. ii. 23.5, pi. 54, fig. 2. 



Alasmodon undidata, Swainson, Lardner's Cab. Cyclop, cxxiii. 288, fig. 61. 



Strophhus scnl/itilis, Stuipsox, Shells of New England, 15 (1851). — The young, Lea. 



Shell transversely-ovate, strong, much inflated, widely gaping ; 

 beaks at the anterior third, very prominent, tumid, with three or 

 four large, concentric, oblique undulations upon them ; anterior and 

 basal margins broadly and regularly curved, with a very slightly 

 lobed appearance in front of the beaks ; posterior margin angular 

 behind the ligament, and pointed at tip, rai)idly narrowed ; liga- 

 mentary area imperfectly marked l)y an ill-defined ridge, which is 

 usually wrinkled in the direction of its course ; margin compressed. 

 Surface a good deal undulated by the stages of growth ; epidermis 

 shining, of a dark olive-color, everywhere rayed with fine lines, al- 



