WHITE.) : CARBONIFEROUS FOSSILS. 165 
This shell is somewhat variable in the convexity of the dorsal valve, 
the distinctness of the dorsal sinus, and the strength of the cardinal 
and brachial processes. 
Position and locality —The upper portion of the Kinderhook division of 
the Subcarboniferous series at Burlington, lowa. A closely similar form 
exists in the upper portion of the Burlington limestone, and another in 
the Keokuk division, but they are at present regarded as distinct. 
Genus RHYNCHONELLA Fischer. 
RHYNCHONELLA OTTUMWA White. 
Plate 41, figs. 5a, b, and «. 
Rynchonella otituwma White, 1862, Proc. Bost. Soc. Nat. Hist., vol. ix, p. 23. 
Shell rather small, variable in outline from subtriangular to subovoid; 
valves nearly equally convex. Ventral valve regularly convex along the 
middle from beak to front, broadly convex across the middle from side te 
side; beak prominent, projecting backward and with an upward curve; 
the space beneath it a little flattened, which gives it somewhat the ap- 
pearance of an area; deltidial pieces occupying arather large equilateral 
triangular space, with a moderately large, oval foramen. Dorsal valve 
broadly convex, umbo depressed. Surtace marked by frem nine to 
eleven somewhat angular plications on each valve, which are absent or 
become obsolete on the posterior third of the shell; two of these plica- 
tions occupy the mesial sinus of the ventral valve and three of them the 
mesial fold of the dorsal valve; the mesial sinus is deep, and ferms a 
more censpicuous feature than the mesialfold. Young examples of this 
shell are nearly plain, but the plications on the older ones are well 
marked. 
Length from ventral beak to front, 12 millimeters; greatest breadth, 
which is in front of the middie, about the same. 
Position and locality.—Saint Louis division of the Subearboniferous 
series, Ottumwa, Iowa, and various other leealities in Lowa, Illinois, and 
Missouri. 
Genus SPIRIFER Sowerby. 
SPIRIFER SUBCARDIIFORMIS Hall. 
-Plate 41, figs. 2a, b, and. 
Spirifer subeardiiformis Hall, 1858, lowa Geol. Rep., vol. i, part ii, p. 660. 
Shell subelliptical in marginal outline, a little wider than Jong; hinee 
line shorter than the greatest width of the shell. Dorsal valve a little 
less convex than the ventral, its beak somewhat prominent and project- 
ing beyond the hinge line; mesial fold rather broad in front, slightly 
elevated, marked by four plications which ail coalesce at the beak; a 
very slight elevation appears in the bottom of the groove which sepa- 
rates the two middle plications of thé fold, and the two grooves which 
separate the fold frum the lateral portions of the valve are breader than 
any of the others; from seven to nine simple, rounded plications mark 
the space on each side of the fold, the inner ones being strong and the 
outer ones becoming obsolete. Ventral valve having its beak prominent, 
incurved, and projecting back further than that of the dorsal valve ; 
mesial sinus bread, not deep, bearing three plications; from seven to 
