40 University of Michigan 



grown, possibly S. acuminatum Pr., but heavy for that species." 



Sphcerimn sulcatum (Lam.). Habitats : 4, 5, ym, 9, 10, 27m. 

 Notably a quiet water species, mainly in mucky or marly 

 bottoms. Often large and globose : 1. 18. i mm. ; alt. 13.9 mm. ; 

 w. 10.6 mm. 



Sphcerium occidentale Prime. Habitat 18. As in Huron 

 County,'* this species was quite abundant in the temporary, 

 swamps. Quite typical: 1. 6.7 mm.; alt. 5.6 mm.; w. 4.2 mm. 



SphcBrium rliomboideum (Say). Habitat 9; Tamarack 

 Lake and outlet. Fragile: 1. 13.2 mm.; alt. 10.2 mm.; w. 

 7.9 mm. 



Sphcerium sp. ? Habitat 24. A single broken valve, 



Musculiiim truncatum (Linsley). Habitats: 13, 15; peren- 

 nial pools. A specimen: 1. 8.1 mm.; alt. 7 mm.; w. 4.4 mm. 



Musculium secure {VnvL\Q). Habitats : 7m, 17. Quite abun- 

 dant in a temporary pond. Mostly small and immature. 



Muscidium rosaceum (Prime). Habitats: 5, 7m, 26. Com- 

 mon in Hancock Creek; an example: 1. 6.5 mm.; alt. 5.7 mm.; 

 w, 3.9 mm. 



Muscidium pusillum Sterki. Habitat 28. Found with Pisi- 

 dium abditum in considerable numbers in a mucky-bottomed 

 cut-off of Hancock Creek. Types of species.^ 



Pisidiurn ahditum Haldeman. Habitats : 22 , 26, 28 , 47. Not 

 typical; those from hardwood spring (22) heavy and globose, 

 with swollen but less projecting beaks, while those from Han- 

 cock Creek (26, 28) were heavy but not so globose and with 

 even less prominent beaks. A specimen from the spring: 1. 4.4 

 mm. ; alt. 3.7 mm. ; w. 2.8 mm. 



Pisidiurn aMne Sterki. Habitats : 6m, 7, 9, 27m. 



* H. Burrington Baker, 191 1, A Biol. Surv. of the Sand Dune 

 Region on the South Shore of Saginaw Bay, Mich. Mollusca. Mich. 

 Geol. Biol. Surv., Publ. 4, Biol. Series 2, pp. 121-176. 



5V. Sterki, 1911. Nautilus, XXIY, p. 3. 



