56 
There is also usually some sign of bifurcation in the plications of the 
lateral Blopes, especially adjacent to the median fold and sinus. Mather’s 
specimens of S . rockymontanus 1 are more accelerated in bifurcation of 
plications than ours; for whereas their average size is the same as the 
majority of ours they have usually 8 plications upon the fold, 7 to 9 in 
the sinus, and frequently 2 to 4 bifurcating upon the lateral slopes, even 
when at times the 1 or 2 plications adjacent to the fold or sinus are simple; 
sometimes also, unlike ours, the plications within the sinus bifurcate. 
Locality and Horizon. Common in the Pennsylvanian throughout 
the Appalachian, Mississippi Valley, Rocky Mountain, and Great Basin 
regions. In the Minnewanka region in the Permian of sections 1-14 (R), 
18 (r); in the Pennsylvanian of sections 1-29 (r); 2 a-3 (c), 10 (c), 
14 (c); 2-1 (r), 2 (c), 6 (c), 11 (C), 12 (C), 14 (r), 15 (r), 16 (r), 17 (r), 18 (c), 
20 (r); 3-6 (r);3a-3 (c), 4 (c). 
Spirifer rockymontanus , Forms A-E 
In the Minnewanka region occurs a great range in the variations of 
this species, and all of them intergrading. These occur in a bed one foot 
thick in section 2-12; so that they are, with two exceptions, undoubtedly 
merely variations of one species and not distinct species. As may be seen 
under “General Discussion of Spirifer rockymontanus,” page 57, it was thought 
best to separate the two variations represented by S . opimus and S. boon- 
ensis as species, since they apparently bred true in some other area, whereas 
the more distinctly defined among the other variations will be noted here 
under the terms Form A, Form B, etc. Owing to the density of the 
limestone the majority of specimens fail to show the finer surface markings, 
lack the cardinal angles, or exist merely as internal moulds. This is 
especially true of the larger individuals. We thus have made no effort 
at the different localities to distinguish between the various forms of 
rockymontanus . 
Form A 
Shell transverse, with hinge-line equalling the greatest width below, 
the lateral margins meeting the hinge-line at a right angle. Plications 
rounded to subangular, one or two adjacent to fold and sinus bifurcating. 
Represented by a to e inclusive in the table under S . rockymontanus , page 54. 
This is the most abundant form in the Minnewanka region. 
Form B 
Shell with length and breadth subequal; cardinal angles rounded. 
Plications rounded to angular, one or two adjacent to the fold and sinus 
bifurcating. This is the form figured under S. rockymontanus from 
Colorado by Girty, and from Pennsylvania by Raymond. In proportion 
of length to breadth it is similar to S. opimus , but this form has lateral 
plications simple and those of sinus and fold rather obscure. It is repre- 
sented by f in the table, page 54. 
1 Loc cit. 
