8 THE NAUTILUS. 



Pisidium spharicum, n. sp Mussel very inequipartite, strongly 



inflated, nearly globular ; superior margin nearly straight, short, pos- 

 terior subtruncate, the others rounded, supero-anterior slope barely 

 marked; beaks near the posterior end, high, prominent over the 

 hinge margin, rounded ; scutum and scutellum distinctly marked ; 

 surface dull to slightly glossy, with fine, irregular strise and a few 

 lines of growth, color yellowish to grayish corneous, lighter along the 

 margins, often with brown to blackish mottlings, whitish to straw in 

 the young ; shell rather strong, posterior muscle scars and pallial 

 lines distinct; hinge stout, curved, cardinal teeth rather small, the 

 right angular, with the posterior part thicker and grooved, the left 

 anterior short, abrupt, angular, the posterior steeply oblique, little 

 curved ; ligament strong. Soft parts not examined. 



Long. 5.6, alt. 5.3, diam. 4.6 mm. (100 : 95 : 82). 



Long. 4.8, alt. 4. diam. 3.4 mm. (100: 84: 71). 



Hab. ; New England to Virginia, Ontario and Wisconsin (?) : 

 Westbrook, Me., collected by Prof. A. H. Norton ; Saco, Me., Dan- 

 vers and Lynnfield, Mass., by the Rev. H. W. Winkley; George R. 

 North, Warren, Knox, Co., Me., by N. W. Fermond: Cambridge 

 and Woburn, Mass., by Wm. F. Clapp. ; Va. oppos. Washington, 

 D. C, Sterki ; Unalitoulin Id., Ont., by Justice F. R. Latchford; 

 Fox River, Wis., by Geo. T. Marston, sent by E. W. Roper (if no 

 label was misplaced ; one of the two specimens in the collection is 

 true, the other is a P. abditum). 



Types : No. 797, Westbrook Me., for full-grown specimens. No- 

 727 Saco Me., and 6641, Lynnfield, Mass., for juv. and adolescent 

 of a smaller form ; yet anyone of the lots in the collection might 

 serve as types. 



This very distinct and characteristic Pisidium has been known 

 for many years, but unfortunately much misunderstood and ill- 

 treated. Generally it has been taken for a form of abditum; the 

 late E. W. Roper named it adamsi, and under that name, specimens 

 are in various collections ; I have named it P. minus, having seen 

 two specimens under that name, in a collection, but from that species 

 it is also distinct, as evidenced by authentic specimens of minus. — 

 From larger forms of abditum it is easily distinguished by the large 

 and prominent beaks situated close to the posterior end of the mus- 

 sel, and the strong hinge. In the young, the superior and supero- 

 anterior margins form a peculiar somewhat angular curve, much as 



