222 
Kirtley F. Mather 
certainty. Its oblique diameter must have been as great as 
55 mm. 
Horizon and locality. Hale formation: East Mountain, Fay- 
etteville, Arkansas (Stations 136, 137, and 149). Morrow for- 
mation: near Choteau, Oklahoma (Station 306). Kessler lime- 
stone: near Brentwood, Arkansas (Station 144). 
TRIGONIID^ 
Genus SCHIZODUS King 
Schizodus morrowensis n. sp. 
Plate XV, figure IJf. 
Description. Shell of medium size, transversely sub-ellip- 
soidal, very inequilateral, length to height about as five to four; 
posterio-dorsal margin convex, produced posteriorly, rounding 
narrowly into ventral margin; ventral margin gently convex, 
rounding broadly into the convex anterio-dorsal margin; left 
valve gibbous, the surface sloping from the umbo abruptly 
toward the cardinal and anterior margins, more gently toward 
the ventral and posterior regions ; beak full and prominent, 
elevated and incurved above the hinge area, situated in front 
of the middle and directed somewhat obliquely forward; sur- 
face of shell smooth except for fine concentric lines of growth. 
Dimensions of type specimen, a left valve, are: length, 25.5 
mm. ; height, 19.5 mm. ; convexity of valve, about 7.0 mm. 
Cardinal and internal characters not known. 
Remarks. This species is founded upon a left valve pre- 
served as an internal cast with a portion of the shell adhering 
anteriorly. It differs so notably in outline from the described 
species of this genus that it cannot be included in any of them. 
Horizon and locality. Hale formation : East Mountain, Fay- 
etteville, Arkansas (Station 136). 
PECTINID^ 
Genus AVICULOPECTEN MacCoy 
Aviculopecten hertzeri Meek 
Plate XV, figure 11. 
1871. Aviculopecten (Streblopteria ?) hertzeri. Meek, Proc. Acad. Nat. 
Sci., Phil., p. 61. 
Lower Coal Measures: Newark, Ohio. 
