138 THE NADT1LU8. 



rounded, posterior and inferior margins forming one curve ; beaks 

 slightly posterior, rounded or somewhat flattened on top, moderately 

 prominent ; surface polished, with very fine, slight striae, color corne- 

 ous, occasionally witti a slight reddish tinge, to clear amber, shell 

 transparent to translucent ; hinge stout, plate rather broad ; right 

 cardinal curved, its posterior part thicker, left anterior with apex 

 pointed, posterior rather short, oblique, well curved ; ligament and 

 resilium short, strong. 



Long. 2.2, alt. 1.9, diam. 1.4 mm. (100 : 87 : 64). 



Hab. : New England to Pennsylvania and Minnesota. Types 

 No. 324 from Hess Lake. Newaygo Co., Mich., collected by Mr. 

 L. H. Streng, received in 1895, then regarded as distinct and named. 

 No. 78977 of the Philadelphia Acad. Nat. Sciences, from Point 

 Pleasant, N. J. (F. H. Brown, Aug., 1890), conform with the types. 

 From various places there are specimens of nearly the same size and 

 appearance, but more or less different in shape: superior margin 

 more curved, beaks narrower and more elevated, the anterior end 

 more angular, e. g. from Graham's Creek, Nepean, Ont., collected 

 by Justice F. R. Latchford in 1911, No. 6812. They appear to 

 represent a variety. 



P. glabellum has some resemblance to small forms of P. splen- 

 didulum St.; the latter is widely distributed, common and very vari- 

 able, but from all its forms, glabellum proved distinct. The hinge is 

 markedly strong and somewhat like that of P. variahih and com- 

 pressum ; the mussel is somewhat like a miniature P. variahih, and 

 it appears to range with that group. 



P. lermondi, n. sp. — Mussel rather small, subequipJlrtite; outlines 

 nearly elliptical along the valve edges, well inflated around the beaks, 

 impressed along the margins, with cutting edges; beaks a little pos- 

 terior, rather small, somewhat prominent over the margin; surface 

 polished, with shallow, irregular striae; color deep corneous to some- 

 what olivaceous, shell transparent to translucent, thin; hinge slight, 

 plate quite narrow; cardinal teeth little curved, the right with its 

 posterior end slightly thicker, left posterior short, quite above the 

 anterior; laminae rather short and slight, cusps in the left valve 

 pointed; ligament and resilium slight. 



Long. 3.4, alt. 3, diam. 2.5 mm. (100 : 88 : 73). 



Hab.: Duck Pond, Warren, Me., collected by Mr. N. W. Lermond 

 (in whose honor the species was named), Sept., 1909. Types No- 



