Fauna of the Morrow Group 
151 
Surface of valve marked by fine, rounded, radiating striae 
which increase in number by bifurcation or implantation and 
are indiscernible when the shell is slightly worn. Very faint 
concentric lines of growth are occasionally present. Shell struc^ 
ture finely punctate. 
Remarks. Kozlowski^^ has recently d/escribed a Chonetes, 
referring it to C. glaber Geinitz, from the Upper Carboniferous 
of Bolivia, which may prove to be conspecific with the shells 
described above. Judging from his excellent figures the two 
forms must be very closely related. Like the Morrow forms, 
those from Bolivia appear to be characterized by a moderately 
strong increase in convexity of the ventral valve near the an- 
terior margin and the origination of the mesial sinus in the 
umbonal region at a distance from the beak. In typical C. 
glaber, as figured by Geinitz^^, the sinus originates on the beak 
of the ventral valve and is slightly sub-angular rather than 
shallowly rounded. 
Horizon and locality. Morrow formation: near Choteau (Sta- 
tion 295), and Ft. Gibson (Station 301), Oklahoma. 
Chonetes laevis Keyes 
Plate VIII, figures 13, 11. 
1888. Chonetes laevis. Keyes, Proc. Acad. Nat. Sci., Phil., p. 229, pi. 12, 
figs. 3a-b, 
Lower Coal Measures: Des Moines, Iowa. 
1891. Chonetes laevis. Keyes, Proc. Acad. Nat. Sci., Phil., p. 246. 
Lower Coal Measures: Des Moines, Iowa, 
1892. Chonetes laevis. Keyes, Proc. Iowa Acad. Sci., vol. 1, pt. 2, p. 22. 
Lower Coal Measures: Near Des Moines, Iowa. 
Keyes's description. ‘‘Shell small; much wider than long; 
transversely semi-elliptical; the cardinal line as long as the 
greatest width of the shell, or often slightly extended beyond 
the lateral margins. Ventral valve convex, with no indication 
of a mesial sinus; beak not prominent; cardinal area rather 
narrow but well defined centrally, becoming linear toward the 
extremities; foramen moderately wide; cardinal margin bear- 
ing from four to seven oblique spines on each side of the beak. 
Dorsal valve flat or very slightly concave with no mesial fold. 
Surface of both valves apparently perfectly smooth ; but under a 
magnifier it is seen to be marked by numerous fine concentric 
striae and more prominent, often somewhat imbricated, lines of 
