Sterki: Some Notes on Sph.eriid^. 435 



partite, little oblique, moderately inflated; outlines nearly elliptical, 

 with the superior margin rather long, nearly straight, the supero- 

 anterior slope slightly marked, the posterior margin rounded or sub- 

 truncate, inferior moderately curved; beaks slightly behind the middle, 

 rather small, rounded, not much projecting over the hinge-margin; 

 surface shining, with very fine, slight irregular striae almost obsolete 

 over the beaks ; color whitish, apparently bleached, and probably 

 glassy colorless when fresh; shell thin, hinge rather long, slight, plate 

 very narrow ; cardinals small, the right slightly curved, its posterior 

 part projecting cusp-like, somewhat thicker and slightly grooved, the 

 left both short, nearly parallel, the anterior close to the hinge-edge, 

 somewhat pointed ; laminse slight, the inner of the right valve with 

 their cusps somewhat pointed and abrupt, the outer ones long, one- 

 half to three-fourths the length of the outer, the anterior with a 

 small, pointed, distal cusp; the left ones with their cusps distal, 

 pointed, abrupt ; ligament rather short, slight, but occupying nearly 

 the whole thickness of the plate. Long. 2.;^, alt. 1.8, diam. 1.3 mm.; 

 long. 2, alt. 1.5, diam. 1.3 mm. (apparently mature). 



Habitat: Wild Cat Lake, Skokomish Valley, Mason County, Wash- 

 ington. Collected by Mrs. Helen T. Gaige in 1919, and sent for 

 examination by Miss M. L. Winslow. The specimens were taken 

 from the digestive tract of a salamander, Notophthalnms torosits, and 

 are all "dead shells," bleached, mostly valves, but a large part other- 

 wise in good condition, with the periostracum and the hinges intact. 

 The mussels were evidently abundant at the place; of nearly three 

 hundred, all, except one, a young shell of Pisidiitm sp. ?, were of this 

 same species, from nepionic young, some still in the parents, to appar- 

 ently full-grown, or nearly so, and fairly uniform. The hinges show 

 some variation : in some specimens the outer laminae of the right valve 

 are rather short ; and in some the cardinals of the left valve are more 

 oblique; and occasionally the posterior is rudimentary. 



The only Pisidhnn, which P. notophthalmi resembles, is tenuissimum 

 (exceptionally small forms), but the mussel is more elongate and less 

 oblique, and the hinge is different. 



Type in the C. M., No. 9229; paratypes in the Museum of Zoology, 

 University of Michigan. 



9. Pisidinm orcasensc n. sp. Mussel of medium size, subequipar- 

 tite. barely oblique, moderately and evenly inflated ; outlines short oval 

 Ann car. mus., xiii., 29, feb. 21, 1922. 



