Sterki : Some Notes on Sph.eriid.e. 433 



man Berry, July, 1909. About thirty specimens were in the lot, rang- 

 ing from young to mature. Types No. 9218, C. M. ; paratypes in the 

 collection of Mr. S. Stillman Berry. 



This modest and rather inconspicuous Pisidium can not be referred 

 to any of the described species, and can not be mistaken for another. 

 Similar specimens have been seen before and set aside with a query — 

 e. g., some from Lynnfield, Massachusetts, collected by H. W. Winkley 

 in 1910, C. M., No. 6645. The color of these is yellowish corneous, 

 and the hinge is slightly different. 



6. Pisidium limpidnm n. sp. Mussel small, subequipartite, short 

 and oblique, moderately inflated; superior margin short, rounded, 

 supero-anterior slope from closely in front of the beaks, somewhat 

 curved, rather steep and long as far as the rounded angular anterior 

 end well below the longitudinal axis; posterior end truncate at right 

 angles, passing into the regularly curved inferior margin without an 

 angle; beaks little projecting over the hinge-margin, slightly flattened 

 laterally near the center, so as to appear almost pointed and closely 

 approximate in frontal (or rear) view; surface polished, with the 

 concentric stride very slight, irregular; shell glassy transparent, color- 

 less when fresh, with a faint yellowish tinge when dry, and a whitish 

 zone along the margins ; hinge rather stout, curved-angular, plate 

 short, rather broad ; right cardinal long, longitudinal, moderately 

 curved in the middle, its posterior end somewhat thicker and slightly 

 grooved to bifid ; the left ones rather small, slight, the anterior nearly 

 straight, its edge pointed, the posterior oblique, slightly curved ; 

 laminse stout, their cusps about in the middle, obtusely pointed, not 

 abrupt ; outer ones about one-third the length of the inner, rather 

 thick ; left ones with their cusps about in the middle, large, pointed, 

 not very abrupt; ligament rather short and thick. Long. 2.5; alt. 2.2,; 

 diam. 1.8 mm. 



Habitat: Elk Creek, one mile south of Oxford Station, Meagher 

 Co., Montana. Collected by S. Stillman Berry, June, 1914. There 

 were over forty specimens in the lot, most of them gravid. They 

 somewhat resemble forms of paiipcrcidiim, but are distinct, differing 

 especially in the features of the hinge. 



Type and additional specimens in C. M., No. 9198 and seqq. ; para- 

 types in the collection of Mr. S. Stillman Berry. 



7. Pisidium apiculatiim n. sp. Mussel inequipartite, oblique, well 



