Fauna of the Morrow Group 
225 
extended though not so much so as valve below^ posterior mar- 
gin and ear not known, but that ear is probably smaller than 
the one in front ; beak prominent and somewhat elevated, 
directed forward with only a very slight obliquity; surface of 
anterior ear sculptured by about 9 radiating striae, coarser and 
somewhat nodose above and becoming finer and smoother below, 
crossed by very fine, close-set, concentric growth lines, both 
striae and growth lines continuing on the surface of the valve 
below the ear but becoming gradually fainter so that to the 
unaided eye the valve appears to be nearly smooth except adja- 
cent to the anterior margin; the growth lines may be traced 
with the aid of a lens over the whole surface so far as known 
but the radiating striae which near the ear originate at the 
beak, become shorter as well as fainter as followed across the 
surface toward the ventral margin, the shortening being 
due to the more marginal origination of each successive stria- 
tion, until they become obsolete at about the middle point of 
the valve. 
The dimensions of the holotype are: length, ±11 mm.; height, 
±13 mm,; convexity of left valve, about 3 mm.; length of hinge- 
line, ±7.5 mm. 
Remarks. This species is founded upon a single, imperfectly 
preserved left valve, but its surface markings are so distinctive 
as to differentiate it clearly from other members of this or 
allied genera. In the absence of the right valve and informa- 
tion concerning its internal characters it is referred provision- 
ally to Aviculopecten although it may prove to be a Deltopecten 
when better known. 
Horizon and locality. Hale formation: East Mountain, Fay- 
etteville, Arkansas (Station 136). 
Aviculopecten? cf. interlineatus Meek & Worth en. 
Several fragments of an Aviculopecten or Deltopecten from 
the locality noted below represent a form closely allied to A.? 
interlineatus. The shells are small, with poorly defined auricu- 
lations and with length of hinge-line only a little less than the 
greatest length of the valve below and at right angles to axis 
of valve; the ventral margin is regularly convex and curves 
equally to the anterior and posterior lateral margins which 
