44 INVERTEBRATA OF MASSACHUSETTS. 



convex as the right, though still shutting considerably within it. 

 Hinge tooth slender, erect ; within smooth ; impressions very- 

 faint. Length | inch, height i inch, breadth | inch. 



Found at Martha's Vineyard, in the neighbourhood of New 

 Bedford, &c. It is abundant about Rhode Island, and is also an 

 inhabitant of the coasts of Georgia and East Florida. 



This species is remarkable for the equality of its valves ; but still 

 they are unequal enough to attract notice at once. The regular and 

 beautifully rounded ribs are also quite characteristic. It bears a close 

 resemblance to Cumingia tdlinoides in its exterior. 



Genus PANDORA, Brug. 



SheU inequivahe, inequilateral, pearly within ; right valve flat, 

 left valve convex ; hinge with two diverging teeth in the flat valve 

 and corresponding grooves in the opposite one. 



Pando'ra trilineata. 



Shell oblong-ovate, rounded before, and with a recurved beak 

 behind. Along the posterior hinge margin of both valves run two 

 rough, elevated, radiating lines. 



State Coll., No. 217. Soc. Cab., No. 1745. 



Pandora trilineata, Say ; Journ. Mad. JVat. Sc, ii. 261. ^mer. Conch., pi. 2. 

 Conrad; Jlmcr. Mar. Conch., 49, pi. 11, f. 1. Lam. ; jSk. sans Vert, vi. 147. 

 Pandora nasuta, SowERBy; Species Conch., f. 18,19. 



Shell pearly-white, ovate, inequilateral, the anterior side broad 

 and regularly rounded, about half the length of the posterior side, 

 which has the hinge margin flattened, straight, or somewhat con- 

 cave, the edge of the flat valve shutting over the edge of the con- 

 vex valve, and terminating in a recurved or ascending tip, its 

 points coarsely wrinkled, irregular, and slightly gaping ; the ante- 

 rior portion of the basal margin has a depending or pouch-like 

 appearance ; the upper edge is margined by two wrinkled, round- 

 ed lines radiating from the beaks, most obvious on the convex 

 valve ; surface wrinkled with undulating lines of growth, and with 

 very faint radiating lines ; sometimes there is a slightly impressed 

 line passing from the beak to the middle of the base. Hinge in 



