356 THE PALEONTOLOGY OF MINNESOTA. 
LDinobolus (%) parvus. 
Dinogoius (?) Parvus Whitfield. 
1882. Dinobolus (?) parvus WHITFIELD. Geology of Wisconsin, vol. iv, p. 347, pl. xxvu, figs. 8-10. 
Fig. 27. Dinoblus (?) parvus Whitfield. A, interior of the dorsal valve as seen in a gutta-percha 
impression, x 2; B, profile view of a cast of the interior, with the thickness and form of the shell indicated 
by the outer line, natural size: C, gutta-percha impression showing the internal characters of the ventral 
valve, x 2; D, cardinal view of the cast of the interior, x 2. 
Description: Shell small for the genus, subcircular in outline, lenticular in 
profile, with the dorsal side somewhat more convex than the other, and both more 
ventricose posteriorly than anteriorly. Posterior margin broadly triangular, curving 
rapidly in the lateral portion to the broadly rounded anterior edge. Each valve 
with a narrow false cardinal area, that of the ventral valve larger and slightly 
produced beyond the dorsal into a samll, acute and but little incurved beak, beneath 
which there appears to have been a narrow, concave triangular depression. 
A gutta-percha impression of the dorsal side of a cast of the interior shows a 
large concave muscular area or platform, oval in outline and produced anteriorly 
into a narrow but slightly elevated mesial septum which terminates near the anter- 
ior margin. Upon this platform, and occupying the greater portion of it, are the 
progressive scars of the lateral muscles, except antero-medially where the anterior 
scar is present; the posterior portion is occupied by two well-defined, parallel, narrow, 
elongate elevations, separated by a narrow sinus, the front of which may be homo- 
logous with the cardinal scars, and the latter with the anal depression of Obolella. 
A crescent so characteristic of Dinobolus does not appear to have been developed in 
either valve. Platform of the ventral valve but slightly elevated, subquadrate in 
outline, widest anteriorly, occupied by broad progressive tracks of the lateral 
muscles, and separated medially by the faintly elevated median scars. Anterior 
edge of platform not excavated. Within the cardinal margin of the ventral valve 
are two short, narrow, rapidly diverging ridges, probably cardinal scars, separated 
by a broad but short pedicle muscle impression. 
