442 Annals of the Carnegie Museum. 



Very variable. There are some doubtful forms, which may, or 

 may not, belong to this species. 



Habitat. — East of the Rocky Mountains, occurring most commonly 

 from New York to Illinois. It is apparently' rare, if occurring at all, 

 in the south. 



Fossil. — Ohio, Michigan. 



17. Musculium truncatum albidum var. nov. 



Mussel of moderate size, with more rounded outlines; surface stripe 

 very slight; shell more or less whitish, translucent to opaque. 

 Habitat. — New York to Illinois. 



18. Musculium truncatum angustatum var. nov. 



More oblique, more inequipartite, the posterior part markedly 

 higher and larger than the anterior; beaks narrow, more elevated and 

 more inclined forward; otherwise near M. albidum. The form, though 

 possibly not of sufficiently wide distribution to constitute a subspecies, 

 is interesting and significant, showing the trend of variation and 

 affinities. 



Habitat. — Canton, Illinois. There are a number of sjjecimcns in the 

 American Museum of Natural History from the Crooke Collection, 

 No. 17,800, and in the Carnegie Museum, No. 7,777- 



19. Musculium lacustre (Miiller). 



Tellina lacuslris Muller, Verm. Hist., II, 1774, p. 204, No. 388. 

 Calyculina lacuslris Clessin, Monogr. Cycladeen in Martini-(?licmnitz, p. 253, PI. 41, 

 figs. 9-12, 16, 17. 



Habitat. — Palearctic and Nearctic Regions. Indiana, Ontario (and 

 probably northward), California, Washington. 



20. Musculium rosaceum (Prime). 



Cyclas rosacea Vkimv., Boston Proc, IV, 1851, p. 155. 

 Sphccrium rosaceum Prime, Mon. Corb., 1865, p. 50. 



\'ery variable. Sphccrium dcjornic 11. F. Carpenter, is a deformed, 

 pathological form of AI. rosaceum. A very small Musculium from 

 northern Ohio, Indiana, and Michigan, which has been taken for 

 immature M. rosaceum, may be M. ryckholti, immature, or possibly 

 distinct. 



Habitat. — Maine to X'irginia, Ontario, Oiiio, and Illinois. 



