MOLLUSCA. 175 



the dominant shells of the temporary swamp habitat (18), probably 

 on account of a similar ability to withstand considerable dessication. 

 It was collected in such places on Sand Point, North and Stony Is- 

 lands, and near Rush Lake. It was also obtainetl, but in lesser 

 abundance, from the ])erennial swamps (19) on Sand Point and near 

 Rush Lake. A large shell measures: length 7.75mm., height 7mm., 

 breadth 4.5mm. 



119. Sphaerium flavum (Prime). — As mentioned above, this species 

 was found in great al)undance in Rush Lake, off Raymond's Point 

 (14). An example measures: length 11.75mm., height 9mm., breadth 

 7mm. The lieaks of the older specimens are considerably eroded. 



120. Musculium truncatum (Linsley). — In this region, this species 

 occurred most commonly, along with Sphaerium occidentale, in the 

 annual swamps (18). It was found in considerable abundance in 

 such places oh Sand Point and near Rush Lake. It was also found, 

 but in lesser numbers, in a perennial swamp (19) on Sand Point, and 

 oE Dune Point (15) and among Sphagnum in a tamarack swamp (42) 

 at Rush Lake. The specimens obtained are small; the largest one 

 measures: length 8mm., height 6.75mm., breadth 4.25mm. 



121. Musculium securis (Prime). — This species was found ciuite 

 abundantly in Turtle Bay (8), in the sand dune lakes along the north 

 shore (9) and in the perennial swamps (19) of Sand Point; in peren- 

 nial swamps on Stony Island and near Rush Lake (19) ; and in an old 

 stone quarry (20) and among Sphagnum in a tamarack swamp (42) 

 near Rush Lake. The shells are small thruout the region, those from 

 the sand dunes especially so, and are labeled "small form" by Dr. 

 Sterki. The largest shell from this locality measures: length 5,5mm., 

 height 4.75nim., breadth 3.25mm. A representative example from 

 another habitat on Sand Point measures: length 7mm., height 6.5mm. 

 breadth 4.25mm.; a more slender, truncate example from Turtle Bay 

 measures: length 6.5mm., height 5mm., breadth 3.75mm. 



122. Musculium partumeium (Say). — A few specimens of this 

 shell were obtained in a temporary swamp (18) on Sand Point and in 

 one near Rush Lake. They are marked "small form" in Dr. Sterki's 

 identification; an example measures: length 8.7omm.. height 7.5 

 mm., breadth 4.5mm. 



123. Musculium ryckhaltii (Norman), var. — A few specimens that 

 were thus identified by Dr. Sterki were collected in a perennial 

 swamp (19) on Stony Island. One measures: length 5.5mm., height 

 5.5mm., breadth 3.75mm. 



Musculium sp? — Shells too young to be identified were collected 

 off Fourth Point (16) at Rush Lake. 



124. Pisidium abditum Haldeman. — A few specimens of this species 



