9 
the apex of the shell the ridge and the shoulder become less prominent 
and the angle between the shoulder and the axis acute as in V. tasgina. 
Finally, near the apex, the ridge and the shoulder fade out entirely. The 
character of the apex and the first few whorls leaves no doubt of the close 
relationship of the species with V. nidaga. The apex is obtuse and the 
first few whorls are quite angular at the base. 
Horizon and Locality. It occurs abundantly at one locality in the 
Willow Creek formation on Willow creek, i.e., centre of sec. 12, tp. 10, 
range 27, W. 4th mer. All the specimens at this locality were from a 
drift flock, but judging from the conditions in the field the writer believes 
that it could not have travelled far from its original position. A few 
specimens were also found in the Edmonton formation on Bow river. 
Dimensions of Type. Length, 27 mm.; width, 20 mm.; apical angle, 
55 degrees. 
Viviparus nidaga sp. nov. 
Plate III, figure 1 
Some of the forms which Meek^ regarded as V. conradi depart rather 
widely from the typical form of the species. They are larger, more elongate, 
and have more rounded whorls. It is possible that they are simply speci- 
mens more advanced in size or age as Meek suggests, but they approach 
V. nidaga, a new species from the Belly Eiver formation, rather closely. 
In Alberta specimens have been found which definitely link the two species. 
The more typical form of V. conradi is represented by Meek’s figures 15a 
and 15b, and the divergent form by figures 15c and 15d. V. conradi is 
rare in the Pale beds, but more common in the Foremost member of the 
Belly River formation. 
Viviparus nidaga differs from V. conradi, the only species from the 
Belly River formation for which it might be mistaken, in the greater 
convexity of the whorls, in the absence of the angle at the base of the body 
whorl, and in the more elongate shape of the shell. The spiral whorls 
of the new species, however, are angular at the base. Certain species 
are clearly intermediate between V. conradi and V. nidaga, leaving no 
doubt of the close relationship of the two species. 
V. nidaga is close to V, leai, which occurs in several post-Bearpaw 
formations, differing chiefly in being larger and more slender in shape 
and in having more angular spiral whorls. It is rare in the Pale beds 
and in the Foremost member of the Belly River formation. The specific 
name means “prairie chicken” in Sarcee Indian. 
Dimensions of Type. Length, 27 mm. ; breadth, 22 mm. ; apical angle, 
60 degrees. 
Several well-preserved specimens of Viviparus prudentius White^ 
were collected on Pincher creek by Weston in 1883, and by Dawson from 
Gooseberry canyon, St. Mary river, in 1881. Both localities are in the 
St. Mary River formation. V. prudentius also occurs in the Willow 
Creek and Paskapoo formations. This species is the culmination of the 
V. nidagor-V. leai-V. prudentius line of development, in which is shown a 
progressive rounding of the whorls and flattening of the spire. 
iMeek: U.S. Geol. Surv., vol. 9, p. 679, PI. 42, figs. 15a, b, c, d (1876). 
2U.S. Geol Surv., 3rd Ann. Kept., p. 467, Pi. 25, figs. 17, 18 (1883). 
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