438 Annals of the Carnegie Museum. 



quite small, vestigial, posterior nearly half as long as the inner, con- 

 nate with it proximally; the left both with their cusps about median, 

 small, very abrupt, nearly spine-like; ligament rather short and thick. 

 Long. 3.3; alt. (over beaks) 2.9; diam. 2.'j mm. 



Habitat: Small swamp near Quamishan, Vancouver Island, British 

 Columbia. Collected by A. W. Hanham. sent for examination by 

 S. S. Berry, 1919. There were only four specimens in the lot, asso- 

 ciated with the preceding species and P. colnmhianum. They are 

 plainly distinct and show only slight differences of shape between 

 themselves. The mussel is so strongly and evenly inflated that a 

 transverse section behind the beaks would be circular, or the diameter 

 may even surpass the dorso-ventral dimension. That the beaks are 

 calyculate is possibly due to some influence of the habitat, and speci- 

 mens from other places may not show this feature. Only one speci- 

 men was opened, but its hinge appeared to be normal. In shape they 

 are somewhat like forms of P. mediannm Sterki, but the beaks are 

 inclined backward, and the hinge is dift'erent. Type in the C. M., 

 No. 9261. 



12. Splicer iiim dcdivc n. sp. In the Preliminary Catalog of the 

 North American Sphseriidse, p. 433. it is stated that a form of 

 Sphccrimn was doubtfully referred to anrcnm Prime. ^ With more 

 materials coming in, it became evident that the form was at least a 

 -well-marked subspecies, which I have named dcdivc. A large num- 

 ber of good specimens from the Sheyenne River, North Dakota, col- 

 lected by members of the University of Michigan in the summer of 

 1919, are evidently the same, and showed conclusively that this 

 Sphcerhnn is different and distinct from anrcnm. 



The mussel is less elongate, the supero-anterior slope is more 

 marked and steeper, the posterior margin is truncate or subtruncate 

 at nearly right angles; both ends are more angular- and more ventral; 



- Old specimens are often of more rounded outlines, and less character- 

 istic ; the same is true with almost all Spha^ria of this group {Cyrenastrum) . 

 the beaks are somewhat anterior and inclined forward, and markedly 

 narrow in the center, as is especially noticeable in half-grown and 

 adolescent mussels, moderately large, somewhat broad, and not so 



1 As described and figured by T. Prime in Mon. Corb., p. 35, and shown 

 in the rather poor specimen (valves) in his collection, not designated as type; 

 origin: "Lake Superior?". 



