Fauna of the Morrow Group 
175 ^ 
the small, triangular ears, the latter sharply demarked from 
visceral portion of valve and quite flat ; beak small and incurved,, 
umbonal region not projecting far behind the hinge-line; venter 
very slightly flattened anteriorly, curving gradually into the 
rounded main flanks laterally ; no mesial sinus present. Surface 
of valve non-costate, marked only by concentric grov^th lines 
which are usually quite conspicuous in all stages of growth and 
sometimes assume the appearance of concentric ribs or wrinkles, 
and studded with the bases of comparatively large erect spines 
irregularly scattered at distances of one to two millimeters from 
each other, over the entire surface of valve. 
Brachial valve unknown. 
Remarks. The distinguishing characteristics of this form are 
the small, flat triangular ears directed at nearly a right angle 
toward the cardinal slopes, and the character of the surface 
markings. Its resemblances to other members of the genus are 
not conspicuously close. 
Horizon and locality. Brentwood limestone: near Brentwood 
(Station 145), and Fayetteville (Station 152), Arkansas. 
RHYNCHONELLID^ 
Genus PUGNOIDES Weller 
Pugnoides triangularis n. sp. 
Plate XII, figures 12-1 2c. 
Description. Shell small, sub-triangular in outline, valves 
gently and sub-equally convex, length and breadth about equal, 
greatest width about one-fourth the distance from anterior 
margin to beak. Dimensions of two perfect specimens are: 
length, 8.0 mm., 6.9 mm. ; breadth, 8.1 mm., 6.7 mm. ; thickness, 
4.3 mm., 3.6 mm. 
Pedicle valve shallow, the point of greatest convexity slightly 
posterior to the mid-length of the valve, the surface sloping very 
slightly toward the anterio-lateral extremities but curving reg- 
ularly toward the anterior margin, the umbonal region broad 
and little elevated, the umbonal slopes low but strongly incurved 
toward the cardinal margin; lateral margins straight or very 
slightly convex, meeting at the beak in an acute angle where the 
posterio-lateral edges of the shell are strongly inflected forming 
a sort of false cardinal area, the lateral margins rounding broadly 
