Sterki: Some Notes on Sph.eriid^. 437 



curved, supero-anterior slope slightly curved, anterior end well below 

 the median line, rounded angular, posterior margin subtruncate pos- 

 tero-anteriorly to rounded, passing into the inferior without any 

 angle ; beaks somewhat posterior, rather small, rounded, little ele- 

 vated; surface dull glossy, with very fine, barely noticeable, irregular 

 striae, and two or three slightly marked rest-lines; color yellowish 

 corneous, shell thin, translucent to transparent ; hinge somewhat short, 

 about three-fifths the length of the mussel, curved, rather slight, plate 

 rather long, narrow ; the right cardinal rather long, moderately, and 

 regularly curved, its posterior part slightly thicker and grooved, both 

 left cardinals a little oblique, rather long, nearly parallel, slightly 

 curved, the posterior passing over the anterior for about two-thirds 

 of its length; the right inner laminae both have the cusps rather distal, 

 pointed, not very abrupt, both the outer laminoe are small and short, 

 or the posterior about one-third the length of the inner, both left 

 lamina; with their cusps distal, very abrupt, spine-like, with the crests 

 somewhat rounded or truncate, inclined distalward; ligament mod- 

 erately long and thick. Long. 3.2; alt. 2.7; diam. 2 mm. 



Soft parts apparently of a yellowish or reddish tinge, as seen in 

 dried specimens. One mussel was almost completely filled with about 

 twenty-two nepionic young, about 0.8 mm. long, and in others the 

 young could be seen through the transparent shell. 



Habitat: A small swamp near Quamishan, Vancouver Island, Brit- 

 ish Columbia, associated with the following, all plainly identical, with 

 slight variation as to size and shape. 



II. Pisidium pilula n. sp. Mussel subequipartite, somewhat elon- 

 gate, strongly inflated, globular; outlines of the valve-edges oval to 

 elliptical, supero-anterior slope barely or not marked; beaks somewhat 

 posterior, narrow, calyculate, rather well elevated and somewhat in- 

 clinjed backward ; surface shining, with striae very fine and slight, 

 shallow, irregular; color pale corneous, lighter inclining to straw- 

 color along the margins; shell thin, translucent; hinge curved, slight, 

 plate short, narrow; cardinals quite small, short, the right slightly 

 curved, with the posterior part abruptly much thicker, bifid ; left both 

 comparatively very short, far apart, the anterior on the edge of the 

 hinge, with its crest pointed, the posterior oblique, barely curved, not 

 extending over the anterior; the right inner laminse both with the 

 beaks about median, small, pointed, bent upward, the outer anterior 



