Sterki: North American Sph.eriid.e. 443 



21. Musculium rosaceum fuliginosum var. nov. 



Mussel small, rather short, subequipartite, moderately inflated, 

 somewhat "pinched" along the margins; beaks nearly in the middle, 

 narrow, somewhat prominent, calyculate; superior margin angular at 

 the beaks, its anterior and posterior parts straight or nearly so, equally 

 sloping; supero-anterior and posterior slopes, or truncations, well 

 marked, nearly straight, the posterior longer and steeper, nearly at 

 right angle with the longitudinal axis, anterior and posterior ends 

 rounded; inferior margin moderately curved; surface shining and 

 with a silky gloss derived from very narrow, membranous, scaly 

 projections of the periostracum on the fine concentric striae; shell 

 very thin, glassy transparent, with a marked grayish or smoky hue. 



The largest specimen measures: Long. 7; alt. 6; diam. 3.8 mm. 



The mussel is striking in appearance and at first sight seems to be 

 distinct, especially since all specimens are remarkably uniform, but 

 young and adolescent individuals reveal features of other forms of 

 M. rosaceum. 



Habitat: — Scott Graham Creek, Carleton County, Ontario, collected 

 by Mr. Justice F. R. Latchford, 191 1 and 1913. Specimens are con- 

 tained in his collection and in the Carnegie Museum, Nos. 6,945 ^''^d 

 7,431. Justice Latchford writes in November, 1913: "No. 2925 is 

 quite common. I have visited the creek at all seasons and never 

 found any larger shells than those which I send; I therefore regard 

 them — the larger ones — as full-grown." 



22. Musculium declive Sterki. 



Musculium declive Sterki, Nautilus, XXV, 1912, p. 103. 

 Habitat: — Michigan, Ontario. 



23. Musculium ryckholti (Normand). 



Cyclas ryckholti NORMAND, Notes sur Quelques Nouvelles Cyclades, 1844, p. 7. figs. 5,6. 

 Calyculina ryckholti Clessin, Monograph Cycladeen in Martini-Chemnitz, 1897, p. 

 257, PI. 40, figs. 20-27. 



Very variable. Some of the forms appear to be the same as vari- 

 eties described from Europe. 



Habitat. — Palearctic and Nearctic Regions. Maine, Connecticut, 

 Ontario, Michigan, Iowa, South Dakota, Montana, Idaho, and prob- 

 ably far northward. 



Musculium pusillum Sterki, cj. Nautilus, XXIV, 1910, p. 3, is 

 probably an immature form of M. ryckholti. The type came from 

 Michigan. 



