454 Annals of the Carnegie Museum. 



39. Pisidium glabellum Sterki. 



Pisidium glabellum Sterki, Nautilus, XXVI, 1913, p. i37- 



Variable. Some of the forms ranged under this species may be 

 distinct. In spite of its minute size, it seems to fall into the same 

 group with P. variabile. 



Habitat.- — New England, New Jersey, Pennsylvania to Ontario, 

 Minnesota, and Manitoba. 



40. Pisidium sphaericum Sterki. 



Pisidium sphcericum Sterki, Nautilus, XXVI, 1912, p. 8. 



This very distinct species has been badly misunderstood, and is 

 found in collections under the names P. abditum Haldeman, adamsi 

 (Roper), minus (Sterki). 



Habitat. — Maine to Virginia, Ontario. 



Fossil. — Maine. 



41. Pisidium adamsi Prime. 



Pisidium adamsi Stimpson, Moll, of New England, 1851, p. 16. 

 Pisidium, adamsi Prime, Mon. Corb., 1865, p. 63. 



Habitat. — Norway, Maine; Holly, Michigan. 



42. Pisidium adamsi affine Sterki. 



Pisidium affine Sterki, Nautilus, XV, 1901, p. 66. 



When P. affine was published, I had seen no P. adamsi, and from 

 the description of the latter it was not evident that the two were of 

 the same species. P. affine is the common, widely distributed, most 

 characteristic form; P. adamsi a somewhat extreme local form, as 

 shown by the specimen in the Prime Collection. 



Habitat.- — Maine to Virginia and Minnesota. 



Fossil. — Ohio, Michigan, Illinois. 



43. Pisidium sargenti Sterki. 



Pisidium sargenti Sterki, Nautilus, XV, 1901, p. 67. 



Moderately variable. 



Habitat.— New England and Pennsylvania to Iowa, Missouri, and 

 Arkansas. 



F05577.— Michigan, Illinois (loess). 



44. Pisidium noveboracense Prime. 



Pisidium noveboracense Prime, Arm. N. Y. Lye, VI, 1853, p. 66, PI. I, fig. 3; Mon. 

 Corb., 1865, p. 67. 



