PLATE LI—Continued. 
EuMETRIA VERA, ViU'. COSTATA, Hall. 
Fig. 27. The cardinal portion of a pedicle-valve; showing the completely coalesced deltidial plates. X 3. 
Fig. 28. A view of a pedicle-valve from which the shell has been partially exfoliated ; showing the faintly 
defined muscular area. 
Figs. 31, 32. Dorsal and profile views of the same specimen. 
Chester limestone. Crittenden comity, Kentucky. 
Fig. 29. A dorsal view of a specimen from which the shell has been exfoliated, exposing the elongate, 
narrow muscular impression of the brachial valve. 
Fig. 30. The upper half of a preparation of the brachidium ; showing in the solid opaque matrix the 
attachment of the crura to the primary lamellfe, and the bifurcate extremity of the loop. X 2. 
Chester limestone. Chester, Illinois. 
Fig. 33. The interior of the umbonal portion of a brachial valve ; showing the posterior horns of the hinge- 
plate, the concave median plate and the elongate, narrow dental sockets. The crural jdates 
and their processes have been lost. X 3. 
Chester group. Crittenden county, Kentucky. 
Eumetria Verneuiliana, Hall. 
Figs. 34, 35. Dorsal and profile views of a specimen with coarse surface plications. 
St. Louis group. Spergen Hill, Indiana. 
Eumetria vera, Hall. 
The umbonal portion of an old shell enlarged to show the thickening of the coalesced deUi<lial 
plates which have become conspicuously protuberant. This thickening has been accompanied 
by a similar growth on the brachial valve which has T-endered the flattened cardinal expansion 
very prominent, as seen on the right of the beak. The growth of the brachial valve has been 
somewhat unsyinmetrical. X 2. 
The umbonal portion of a specimen which has been broken longitudinally nearly in the median 
axis. On the upper portion is exposed the suj-face of the more distant of the two crural plates, 
flattened below by the transverse concave plate and the upward extension of the nearer of the 
crural plates. The outer shell is retained about the beak of the pedicle-valve. X I 5 . 
Chester group. Crittenden county, Kentucky. 
The distinction between the three forms of Ecmbtria here represented is one not easy to carry out 
with an abundance of material. Eumetria Verntuiliana was founded upon the small, very 
finely plicated shells from the white limestones at Spergen Hill, Ind., but it was suggested in 
the original description that the larger shells occurring in a silicified condition at the same 
locality and elsewhere, are of the same species. E. vera was based upon specimens of about 
the same size as the latter, with a somewhat coarser plication, derived from the Kaskaskia 
(Chester) limestone at Chester, Illinois, and E. vera, var. costata on lai’ger and more coarsely 
plicated shells from the same locality. It is very frequently difficult, notwithstanding the slight 
differences in geological horizon, to distinguish the huger form of E. Verneuiliana from the typ¬ 
ical form of E. vera, while a distinction between the two forms of E. Ves'neuiliana occuring at 
Spergen Hill is often more readily made. 
Genus ACAMBONA, White. 
Page 119. 
AcAMBONA ? OSAGENSIS, StVulloW. 
A dorsal view of an imperfect specimen of the Retzia Osagensis, Swallow, which will probably 
prove to belong to this genus. 
A portion of the surface of the shell enlarged. The lower part of the figure represents the puncta- 
tions of the outer surface, where it has been exposed and somewhat weathered ; above is the 
surface of one of the inner layers covei-ed with fine pustules. The plications are much more 
distinctly defined on the inner layers, but they are not obsolete on the outer layer as here 
represented. X 5. 
Choteau limestone. Pike county, Missoun. 
Acambona prima, White. 
Figs. 40, 41. Dorsal and profile views of an incomplete specimen which is regarded as belonging to this 
species. 
Burlington limestone. Burlington, Iowa. 
Fig. 38. 
Fig. 39. 
Fig. 36. 
Fig. 37. 
