New Lamellibranchiata- — Ulrich, 
277 
high and 13 mm. thick. Tlie hight is proportionately some- 
what greater in specimens preserving the shell. 
This species has been confounded with M. modiolaris Con- 
rad, by the Kentucky geologists. It is, however, quite a dif- 
ferent species, being proportionally shorter, with a more ar- 
cuate cardinal margin, shorter and wider hinge plate, more 
nearly terminal beaks, and a different outline, the basal mar- 
gin in Conrad's species being always more or less sinuate 
whereas it is convex in M. oviformis. Other differences might 
be mentioned, but these will suffice. 
Position and locality : This species is very abundant in the argilla- 
ceous strata overlying the lower massive limestones of the Trenton of 
central Kentucky, at Burgin, Danville and Frankfort, Ky. 
Modiolopsis simulatrix, n. sp. 
Fig. 5, Modiolopsis si7inilatrlx, n. sp., Cincinnati group (lower beds) 
at Covington, Ky. a, b and c, three views of a si)ecimen of this species 
which preserves the shell. The postero-cardinal region should be a 
little more angular than shown. 
Shell a little beloAv the medium size, transversely subovate 
in outline, widest posteriori}-. Valves moderately convex, 
with point of greatest convexit}' somewhat above and in front 
of the middle. Anterior end short,not appreciably contracted, 
rounding almost regularly from the beaks into the nearly 
straight or slightly convex basal margin. Posterior margin 
the most prominent at a point a little below the center, but not 
greatly so, the curve on the whole being nearly equal from the 
basal margin to the posterior extremity of the slightly arcuate 
hinge line, where the outline is often subangular. Beaks small 
not projecting above the hinge line, situated about one-sixth 
of the length of the shell from the anterior extremitj'. Um- 
bones rounded. Surface between the umbones and the basal 
margin transversely flattened, but not sinuate ; cardinal slope 
flat or slightly concave. Entire surface marked with two sets 
