464 Annals of the Carnegie Museum. 



Habitat. — Ontario and Ohio to South Dakota. 

 Fossil. — Ohio. 



loi. Pisidium pauperculum sulphureum var. nov. 



Less high, oblique, somewhat rhombic in outline, little to moderately 

 inflated; beaks little elevated; superior margin less curved than in 

 other forms of P. pauperculum, inferior little curved to nearly straight; 

 surface polished; color light to sulphur-yellow in fresh, brownish in 

 dead shells; hinge slighter, and somewhat different, especially the left 

 anterior cardinal tooth, which is shorter and more abrupt anteriorly. 

 Markedly different from the other forms of P. pauperculum, and 

 possibly a distinct species. 



Habitat. — Mountain Lake and Ives Lake, Marquette County, 

 Michigan, and " Marquette County," collected by Mr. Bryant Walker 

 in 1898, 1906, and 1900; Brooks Lake, Newaygo County, Michigan, 

 collected by Mr. L. H. Streng in 1899; Lake Nipissing, Ontario, 

 collected by Justice F. R. Latchford in 1913 (Carn. Mus., No. 7463). 



102. Pisidium ovum sp. nov. 



Mussel of medium size, inequipartite, somewhat oblique, strongly 

 and evenly inflated, nearly globular; beaks markedly posterior, large 

 and broad, rounded, not mamillar, moderately prominent; superior 

 margin short, nearly straight, bounded by angles which are only 

 slightly marked in some adult, but well-marked in young and adoles- 

 cent mussels, as to the rest of the outline oviform, with the anterior 

 end rather broadly rounded; surface more or less glossy, with fine 

 to very fine, irregular concentric stria? and several lines of growth at 

 irregular intervals; color straw to deep corneous; shell thin, trans- 

 lucent; hinge slight, short, plate very narrow; cardinal teeth small, 

 the right moderately curved, its posterior part thicker, both left 

 teeth cjuite short and markedly abrupt, the posterior oblique and 

 slightly curved; laminae rather short and slight, outer ones in the 

 right valve quite small; cusps placed rather proximally, with very 

 steep slopes, si)ine-likc, pointed; ligament moderately long, rcsilium 

 slight. 



M EASUREMENTS. 



Long. 4.8; alt. 4.2; diam. 3.5 mm. (100 : 88 : 73). 

 Long. 4. ; alt. 3.3; diam. 2.7 mm. (100 : 82 : 67). 

 Long. 3.5; alt. 3. ; diam. 2.4 mm. (100 : 86 : 67). 



