65 
Pedicle valve strongly convex, with its greatest convexity in the 
umbonal region, the surface curving from this region very abruptly, 
forming almost a straight line, to the cardinal extremities; anteriorly it 
curves less aburptly with a greater convexity. Beak pointed and incurved. 
Cardinal area high, gently arched above, almost straight below, this 
latter part making an angle of about 90 degrees with the plane formed 
by the junction of the valves; delthyrium forming an equilateral triangle, 
the upper third of which is covered by an almost flat, slightly convex 
pseudo deltidium. The cardinal area on each side of the delthyrium is 
bisected by a straight, slightly raised line which extends obliquely out 
from the beak to the hinge-line; the space within these lines is the true 
cardinal area and is vertically striate, beyond them the false cardinal 
areas round gradually into the lateral slopes of the valve. Median sinus 
originates at the beak, becoming broad, evenly rounded, and of moderate 
depth anteriorly; the anterior prolongation which extends into the fold 
of the opposite valve is in large shells, subparallel with the cardinal area; 
three low plications present, a single median and two lateral ones. Lateral 
slopes of the valve each bearing from 8 to 10 low, rounded, simple plications; 
these are more or less obscure and are entirely wanting towards the cardinal 
extremities. Internally the dental lamellae are prominently developed; 
with divergence similar to that of the sides of the sinus they extend with 
lessening strength in a straight line almost half-way from the beak to the 
frontal margin of the valve where, before disappearing, they bend towards 
each other so as to partly enclose the faint muscle impressions; pos- 
teriorly these plates are united by the delthyrial plate, which, confined 
to the upper third or half of the delthyrium, is slightly depressed below 
the level of the cardinal area. 
Brachial valve Bomewhat less convex than the pedicle, its greatest 
convexity near the middle of the valve, the convexity extending regularly 
to the front and sides of the valve except at the cardinal angles which are 
slightly flattened. Beak incurved. Median fold rather narrow, becoming 
high anteriorly, rather narrowly rounded and not prolonged anterior to the 
parts of the valve bounding it; this gives to the front of the shell a truncate 
appearance, making the anterior and posterior sides of the shell subparallel. 
Median fold with two low plicat’ons; lateral plications similar in form and 
number to those of the opposite valve but somewhat stronger. 
The finer surface markings consist of concentric growth lines which in- 
crease in strength anteriorly, and of rather conspicuous, fine, radiating papillae. 
Remarks. This genus differs from Syringothyris in the absence of 
a syrinx; from Pseudosyrinx in its lower and more arched cardinal area, 
and in its shorter hinge-line and more rounded cardinal extremities. 
Pseudosyrinx missouriensts from the Burlington of Missouri has a 
much more elevated and straighter cardinal area, with its margins much 
more narrowly rounded, and has also more (16) plications upon each side 
of fold and sinus. Spiriferella negleda is similar to S. minnewankensis 
in the broadly rounding margins of the cardinal area; it differs from 
it in being more elongate, in having a single faint broad plication in the 
sinus and only six lateral plications upon each side of fold and sinus, in 
its more elevated median fold, which is much more produced anteriorly, 
and in the somewhat greater angle between the cardinal area and the 
plane formed by the junction of the valves. 
