8 THE NAUTILCS. 



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 stria3 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 



