Sterki: Some Notes on Sph.5;riid^. 431 



curved; laminae at marked angles to the plate, massive, the right inner 

 both with their cusps about in the middle, obtusely angular, not 

 abrupt ; outer anterior nearly half as long, the posterior less than one- 

 third as long as the inner, left both with their cusps markedly larger, 

 pointed, somewhat more abrupt; ligament short, thick. Long. 3.5; 

 alt. 3.4: diam. 2.6 mm. Long. 2.8; alt. 2.8: diam. 2 mm. (apparently 

 mature). 



Habitat: Lake Winnecook, Unity, Maine. Collected by S. Still- 

 man Berry in 1909. There were twenty-two specimens in the lot, 

 ranging from young to old, and remarkably uniform, except that in 

 a few old ones the supero-anterior slope and the posterior margin are 

 slightly curved. 



In shape and appearance the mussels somewhat resemble P. vari- 

 abilc, especially immature examples of the form ciccr, but are much 

 smaller and easily distinguished; the young are of a different shape 

 from those of variabilc. 



Types No. 9214, C, M. ; paratypes in the collection of Mr. S. Still- 

 man Berry. 



4. Pisidiitiii paradoxitm n. sp. Mussel of medium size, somewhat 

 inequipartite and oblique, moderately elongate, moderately inflated, 

 having somewhat oval outlines; superior margin nearly straight, 

 bounded by slightly marked angles anteriorly and posteriorly, the other 

 margins rounded, the supero-ailterior slope barely marked in the 

 adult, somewhat more so in the young; beaks slightly posterior, 

 rather small, moderately projecting, rounded; surface with a some- 

 what silky gloss, striae irregular, crowded, very fine, sharp, some of 

 them with the periostracum slightly projecting, scale-like; color uni- 

 formly pale corneous to drab; shell very thin, subtranslucent ; hinge 

 slight, plate narrow; right cardinal with its anterior part nearly 

 straight and longitudinal, close to the valve-margin, thin, the posterior 

 part abruptly bent down, short, strongly bifid, the anterior (or inner) 

 shank forming a hook, the posterior standing out somewhat wing- 

 like ; left cardinals small and short, far apart posteriorly, the anterior 

 nearly straight and longitudinal, the posterior oblique ; laminae rather 

 slight, the inner of the right valve with the cusps small, pointed, 

 about median, the outer anterior placed proximally, about one-fourth 

 the length of the inner, the posterior nearly half as long as the inner, 

 both left laminae with the cusps small, pointed, the anterior abrupt. 



t-'"- 



