50 
Remarks. This species was founded upon several pedicle valve3, the 
brachial being unknown. Of the two specimens figured by Hall and 
Whitfield one has the median sinus smooth, the other shows three faint 
plications beginning near the middle of the shell, a median one and two 
lateral ones, the latter appear to represent branches of the bounding 
strong plications; in the Minnewanka specimens the lateral plications 
usually enter the sinus before the median one as they apparently do in 
the figures cited. Not only in the character cited but in all essential 
particulars does the Minnewanka form agree with this species. Our 
section likewise shows it to be a good species, and not a variety or a tem- 
porary stage in development, for though S. centronatus passes through 
this stage in its youth, as Girty showed in his Yellowstone National Park 
report, 1 this very recapitulation indicates an ancestral state when this 
youthfiul condition was the adult form. The time of the adulthood of 
S . albapinensis seems partly to be represented by the deposition of the 
200 feet of limestone forming section 2-35. That this does not represent 
its entire range is shown first by its sudden appearance at the base of 2-35, 
indicating migration into this region, since no species exists in the lower 
beds which could have evolved into it, and second, a few individuals 
exist in 2-35, accelerated into almost the typical centronatus form. The 
typical centronatus does not appear in abundance until after the deposition 
of 380 additional feet of limestone. 
Spirifer biplicatus Hall from the Kinderhook of Mississippi valley is 
smaller, with mucronate extensions to the hinge-line and with the broad 
plications bounding the medial sinus always simple. S. albapinensis 
resembles more closely S. biplicoides Weller from the Kinderhook of the 
same region, since this species has the large plications bounding the median 
sinus dividing unequally, the smaller branch entering the sinus, but this 
species also is smaller and has mucronate extensions to the hinge-line. 
S. centronatus semifurcatus Girty from the lower part of the Madison of 
Yellowstone National park differs only slightly from this species, if it is 
not identical with it; as the proportion of length to breadth is similar the 
only difference appears to be, judging from the brief description, the figures 
of a brachial valve, that the plications are somewhat stronger in Girty's 
variety. This character is variable in the Minnewanka specimens; a 
few complete individuals show the typical, semi-furcatus brachial valve 
with its prominent median fold divided by a furrow and the typical pedicle 
valve of albapinensis. 
Locality and Horizon. Lower Mississippian of Utah, Nevada, and 
Wyoming. In the Minnewanka region in the Lower Mississippian of 
sections 2-35 (C), 4-3 (c). 
Spirifer ienuimarginatus Hall 
1858. Spirifer ienuimarginatus Hall, Geol. Iowa, vol. 1, pt. 2, p. 641, PI. 20, 
figs. 1 a-c; Spirifera tenuimarginata Hall, 1863, Kept. N.Y. State 
Geol. for 1882, PI. (32) 57, figs. 4-6; Spirifer ienuimarginatus Hall 
and Clarke, 1895, Pal. N.Y., vol. 8, pt. 2, PI. 32, figs. 4,6; Weller, 
1914, State Geol. Surv., 111., Mon. 1, p. 355, PI. 48, figs. 1-5. 
i Loc. cit. 
