152 
Kirtley F. Mather 
growth ; these are sometimes crossed by fine, nearly obsolete, 
radiating striae. Length, 7 mm. ; breadth, 12 mm.’’ 
Remarks. Three pedicle valves and one brachial valve of 
this species are in the Morrow collections. All four are nearly 
fiat and there is no suggestion of fold or sinus. 
Horizon and locality. Hale formation: East Mountain, Fay- 
etteville, Arkansas (Station 136). Morrow formation: near Ft. 
Gibson, Oklahoma (Station 301). 
Genus PRODUCTUS Sowerby 
Productus morrowensis n. sp. 
Plate X, figures l-4a. 
Description. Shell medium to large in size, a little wider 
than long, strongly and regularly arched from beak to anterior 
margin; hinge-line nearly or quite as long as greatest width 
of shell. The dimensions of the holotype and three other speci- 
mens are: 
Length of hinge-line 28.0 mm., ±28.0 mm., ±24.0 mm., ±14.5 mm. 
Distance from hinge-line 
to anterior margin 20.6 mm., 21.0 mm., 17.8 mm., 15.0 mm. 
Distance from umbonal region 
to anterior margin 24.0 mm., 27.5 mm., 26.8 mm., 18.3 mm. 
Convexity of the pedicle 
valve 15 mm., 14 mm., 14 mm., 11 mm. 
The dimensions of the allotype^® and two other brachial valves 
are : 
Length of hinge-line 21 mm., 23 mm., 18 mm. 
Length (perpendicular to hinge-line) of 
visceral portion of valve 12.2 mm., 12.2 mm., 11.0 mm. 
Depth of concavity of valve 10 mm., 6 mm., 8 mm. 
Pedicle valve gibbous, strongly convex but not geniculate, 
more or less produced anteriorly depending on age of indi- 
vidual but only moderately extended even in old age. Beak full ' 
and tumid but not notably extended. Ears gently arched trans- 
versely, of medium size, and with cardinal angles closely ap- 
proximating 90° ; separated from cardinal slopes by sharply 
defined sub-angular depressions. The convergence of the latter . 
depends upon the rapidity with which the umbo enlarges an- 
teriorly and varies somewhat in different individuals. The 
umbonal angle does not depart far, however, from 115°. In 
the umbonal region the surface is regularly convex transversely 
