Sterki: North American Spii.eriid.i;. 461 



84. Pisidium vexum sp. nov. 



Mussel small, slightly inequipartite and oblique, rather well inflated; 

 beaks slightly posterior, rather broad, more or less flattened on top, 

 moderately prominent, descending abruptly toward the posterior part; 

 superior margin nearly straight, bounded by angles, posterior margin 

 subtruncate or rounded, passing into the moderately curved inferior 

 without an angle, anterior end rather broadly rounded, supero- 

 anterior slope marked, nearly straight; surface dullish to somewhat 

 shining, with very fine and slight subregular stria?. Shell thin, trans- 

 lucent to transparent, colorless; hinge rather slight, but well-formed, 

 moderately long, plate rather narrow; cardinal teeth rather long, the 

 right curved to nearly straight in its middle, its posterior end thicker 

 and grooved to bifid, left anterior more curved (in plane), not much 

 bent upward, posterior long, nearly straight and little oblique; 

 laminae: right anterior inner rather long, its cusp nearer the cardinal; 

 outer short; posterior both short; left: both with the cusps rather 

 abrupt, pointed; ligament short, resilium rather stout. 



Measurements. — (Specimen from Ontario) Long. 2.5; alt. 2.1; diam. 

 1.5 mm. (100:84:60). (Specimen from Massachusetts) Long. 3; 

 alt. 2.5; diam. 2.1 mm. (100 : 83 : 70). 



P. vexum is somewhat like P. inoniatuni in size and shape, but more 

 inflated; the shell and hinge are slighter, and the depressed beaks 

 distinguish it. 



Habitat. — Lake Gorman, Renfrew County, Ontario, collected by 

 Justice F. R. Latchford, August 29, 1913. Types are in Justice 

 Latchford's Collection and in the Carnegie Museum, No. 7455. One 

 specimen, somewhat larger, was collected in Hounds Ditch, Duxbury, 

 Massachusetts, by Mr. William F. Clapp in 1913. 



85. Pisidium ohioense Sterki. 



Pisidium ohioense Sterki, Nautilus, XVII, 1903, p. 20. 



Habitat. — Maine, Massachusetts, Ohio, Michigan, Ontario. 



86. Pisidium splendidulum Sterki. 



Pisidium splendidulum Sterki, Nautilus, XI, 1898, p. 113. 



One of the commonest species and very variable; a few of the main 

 forms are named. 



Habitat. — Maine to Virginia and Minnesota. 



Fossil. — Maine, Ohio, Michigan, Illinois. 



