LAMELLIBRANCHIATA. 545 
Cyrtodonta cingulata.] 
incurved ini casts of the interior; in the shell projecting very little above the hinge 
line. Umbonal ridge very indistinct, with the point of greatest convexity a little 
above and in front of the middle. In the casts there is a more or less sharply defined 
and unusually wide depressed or flattened strip running from the beaks downward. 
Hinge plate wide and strong, with two strong posterior lateral teeth in each valve, 
and sometimes a third small oné above them in the left valve. Anterior teeth con- 
sisting of one long tooth placed parallel with the margin of the shell in front of the 
beaks and five or six small unequal teeth running downward from the horizontal 
tooth. Ligamental area well developed. Anterior muscular scar distinct, elongate, 
vertically disposed, situated immediately beneath the cardinal teeth. Posterior scar 
illy defined. Shell substance thin, except in the anterior and dorsal region. 
The small vertically arranged anterior teeth, and the erect and strongly com- 
pressed beaks of casts of the interior are the two principal peculiarities of the 
| species. These and other equally obvious characters distinguish it from C. glabella 
Ulrich. C. saffordi Hall, sp., often has the cardinal teeth broken up in a similar 
manner, but differs too obviously in other respects to render confusion between 
them at all likely. 
Formation and locality.—T wo opposite valves were collected by Mr. Chas. Schuchert at Janesville. 
Wisconsin, in the ‘‘ Lower Blue limestone.” These are now in the museum of the Geological and Natural 
History Survey of Minnesota. 
Mus. Reg. No. 8324. 
CyrtopontTa cinguLaTA Ulrich. 
PLATE XL, FIGS. 7 and 8. é 
Cypricardites cingulata ULRICH, 1892. Nineteenth Ann. Rep.,Geol. and Nat. Hist. Sur. Minn., p. 235. 
Shell scarcely reaching the medium size, ventricose in the central and umbonal 
region, oblique, narrow anteriorly and broadly rounded posteriorly; the outline on 
the whole, excepting a slight prominence at the postero-cardinal edge, almost regu- 
larly ovate; hinge line rather short posterior to the beaks, slightly convex. Beaks 
of good size, strongly incurved, projecting well above the hinge, situated a little 
more than one-fourth of the entire length behind the anterior extremity; umbones 
prominent, full, with an obtuse ridge or line of greatest altitude running from the 
beaks towards the postero-basal side; anterior and ‘cardinal slopes both slightly 
concave, the latter descending more rapidly. Point of greatest convexity near the 
middle of a line drawn parallel with and one third of the hight of the shell beneath 
the hinge. Surface marked with very fine concentric lines, easily abraded, and 
distant irregular lines or wrinkles of growth. Shell substance thin. Internal char- 
acters unknown, 
—35 
