Fauna of the Morrow Group 
217 
Dimensions of type specimen, a left valve, are: height, 6.2 
mm. ; width, 12.5 mm. ; length of hinge-line, 8.4 mm. ; convexity 
of valve, about 2.5 mm. 
Remarks. This species is based upon a single specimen, a 
left valve from the Brentwood limestone. It can hardly be other 
than a Cypricardinia although its outlines are quite distinct from 
those of C. carbonia, the only Pennsylvanian member of the 
genus which is commonly found in the Mississippi valley. The 
smoothness of the surface of the valve at hand is possibly in 
part the result of its weathered condition and it may prove that 
the concentric markings are lamellose and cancellated as is the 
case in many species of this genus. 
Horizon and locality. Brentwood limestone: near Fayette- 
ville, Arkansas (Station 135). 
PTERIID^ 
Genus MONOPTERIA Meek 
Monopteria? sp. 
Plate XV^ figure 9. 
Two fragments of left valves seem to resemble closely the 
forms which have been grouped in the genus Monopteria 
although they cannot be referred to it with certainty. The um- 
bonal ridge is fairly strong and very oblique, approaching the 
hinge-line at an angle of 25° or 30°. The hinge-line is much 
produced posteriorly and, as restored from the growth lines, 
probably projected farther than the posterior portion of the 
shell below. The material at hand does not warrant drawing 
any conclusions as to affinities with the described species of the 
genus. 
Horizon and locality. Hale formation East Mountain, Fay- 
etteville, Arkansas (Station 136). Morrow formation: south- 
east of Ft. Gibson, Oklahoma (Station 303). 
Genus PSEUDOMONOTIS Beyrich 
Pseudomonotis precursor n. sp. 
Plate XV, figures 1, la. 
Description. Shell small, inequivalve, irregularly sub-ovate 
in outline, higher than long, hinge-line half as long as greatest 
