35 
Genus, Schellwienella Thomas 
Remarks. Streptorhynchus King has similar internal characters, but 
the shell is biconvex and the umbo of the pedicle valve is distorted, due to 
the attachment of the shell by its apex. Schuchertella Girty, as shown by 
its genotype S. lens (White), with similar internal characters and bicon- 
vexity, is unattached and un distorted. Orthothetes Fischer de Waldheim 
and Derby a Waagen include both sub-plane to bi-convex shells with 
dental lamellae and a median septum in the pedicle valve, but the former 
has a small pyramidal spondylium, formed between the joined dental 
lamellae and deltidium, which is lacking in the latter. 
Schellwienella inequalis (Hall) 
1858. Orthis inequalis Hall, Geol. Iowa, vol. 1, pt. 2, p. 490, PI. 2, figs. 
6a-c; Streptorhynchus equivalvis Hall and Whitfield, 1877, U.S. 
Geol. Expl. 40th Par., vol. 4, p. 252, PI. 4, figs. 1, 2; Orthotetes 
inaequalis Hall and Clarke, 1892, Pal. N.Y., vol. 8, pt. 1, PI. 9A, 
figs. 20-23; Girty, 1899, U.S. Geol. Surv., Mon. 32, p. 522, PI. 
68, fig. 3a; Schellwienella inequalis Weller, 1914, Geol. Surv., 
Illinois, Mon. 1, pt. 61, PI. 3, figs. 14-16. 
Remarks. This is the most abundant Orthoid shell in the Minnewanka 
region. It is larger than the typical Mississippi Valley form, whose average 
length and breadth, as given by Weller, are 23 mm. and 31 mm. The 
brachial valves accompanying the rather uniform pedicle valves are of 
two kinds— those with a somewhat prominent umbo similar to those from 
the type locality in Iowa, and those with a flattened umbonal region. 
Girty also notes 1 these two types in the Yellowstone National park. Better 
preserved material, with the valves in contact, might enable these two 
forms to be distinguished, but with the material at hand they appear to 
intergrade. The only way in which the pedicle valves differ from the 
Iowan form is in the delthyrium having height and width nearly equal 
instead of being wider than high, and in the more posterior origin of the 
concavity. In the lower beds, sections 2-29 to 2-35 inclusive, the pedicle 
valve is similar to those from the type locality in that the concavity origin- 
ates much nearer the anterior margin, the rest of the valve being fiat. 
Schellwienella inflata (White and Whitfield), similarly from the Lower 
Mississippian, has a very ventricose brachial valve, with the delthyrium 
of the pedicle valve much higher than wide. 
Locality and Horizon. In the Lower Mississippian of Mississippi valley 
and the Rocky mountains. In the Minnewanka region in the Mississippian 
of section 2-22 (C), 23 (c), 24 (c), 25 (c), 26 (R), 28 (r), 29 (r), 32 (r), 35 (r). 
Schellwienella lata n. sp. 
Plate VI, figures 7, 8 
Description. Shell concavo-convex, of medium size, slightly wider 
than long, with greatest width about mid-length ; the hinge-line a little 
shorter than the greatest width; cardinal extremities angular. The dimen- 
sions of a pedicle valve of medium size are: length 13 mm., greatest width 
17 mm., length of hinge-line 16 mm., height of cardinal area 2*5 mm. The 
dimensions of a large brachial valve are: length 14 mm., greatest width 
21 mm., length of hinge-line 18 mm,, convexity 4 mm. 
tLoo.cit. 
