96 
IOWA ACADEMY OF SCIENCE Vor. XXIX, 1922 
crease in height anteriorly and becQme suppressed before reaching 
the margin ; in most specimens the sinus narrows gradually to the 
front, becoming rather acuminate in extreme specimens. Postero- 
lateral angles prominent — viewed brachially, as in figures 1-4, 
there is but little slope from the beak to the angles — but viewed 
ventrally, as in figures 5-8, the postero-lateral edges form an ob- 
tuse angle at the beak which is pointed and incurved over that of 
opposite valve; pedicle opening round and small. Posterior part 
of valve smooth; near the midlength of the sinus there arise two 
(rarely three) plications which become stronger anteriorly, whose 
courses are subparallel and which meet those of the opposite 
valve in such a way as to make the anterior part of the linguiform 
extension sharply denticulate. Just in front of each postero- 
lateral angle and near the margin of the valve are two short 
angular plications. Internally the dental lamellae are short and 
the valve lacks a median ridge. 
o 
O 
C 
Fig. 1. A series of five cross-sections of the rostral part of the shell of Pugnoides 
altus showing the dental lamellae of the pedicle valve and the median septum, crural 
cavity, and crura of the brachial valve (x2j4). 
Brachial valve high, midline gently curving; the sides of the 
valve slope rapidly to the margins; in a side view the outline of 
the valve is sub-triangular; the high mesial region is accentuated 
on the front half by the presence of a sharp angular plication on 
each side of which is another plication equally angular but less 
strong. On the postero-lateral areas arise two or three low pli- 
cations which are directed sharply outward to the posterior margin 
where they alternate with the shorter plications of the pedicle valve. 
Surface of valve smooth. Internally is a well developed septum 
which is divided to form a short crural cavity. 
Position and localities: Lime Creek shales; very common at 
Bird Hill ; also found at the exposures west of Rockford, and 
at Hackberry Grove. A single specimen of smaller size and with 
somewhat different arrangement of the plications is in the Calvin 
Collection from the Independence shale, at Independence. Two 
specimens, one larger than any found in the Lime Creek beds, 
have been collected at exposure No. 3, of the Independence shale 
near Brandon. These have four plications on the fold. 
