PLATE 37. 
Legend: f. Foramen. hp. Hinge-plate. 
c. Crura. dp. Deltarium. 
er. Crural plates. p’. Anterior horn of hinge- 
te. Posterior horns of hinge-plate. plate. 
EUMETRIA, Hatt. 
Page 795. 
Eumerria VERNEUILIANA, Hall. 
Fig. 1. Dorsal view of an orbicular, finely lineate example. 
Fig. 2. The interior of the cardinal region of articulated valves, viewed with 
the plane of the hinge horizontal. This preparation shows in the 
background the large foramen and below it the flattened inner sur- 
face of the coalesced deltidial plates. On either side are the elon- 
gate teeth. The division of the hinge-plate into an anterior and 
posterior portion is seen, the former taking the form of a crescent, 
its horns lying back upon the inner surface of the deltarium; this is 
connected laterally with the socket-walls and anteriorly with the 
anterior tent-shaped portion of the plate, which consists of two deep 
and broad lateral lamellz resting on the bottom of the valve, united 
above by a deeply concave horizontal plate. The divergent and 
greatly elevated crural processes arise from the anterior angles 
formed by the union of these plates. In this figure the anterior 
portion of this apparatus is considerably foreshortened. X 10. 
Figs. 8,4. Dorsal and profile views of a specimen with coarse surface plications. 
Fig. 6. The umbonal portion of an external cast ; showing the maximum devel- 
opment of the foraminal tube which is 
but a slightly introverted lamina. The 
drawing was also intended to show the 
hinge-line, the coalesced deltaria and 
the aliform cardinal expansions of the 
brachial valve, but as the figure is imper- 
fect a corrected cut of the specimen is here introduced. 
Fig. 10. The detached brachidium, viewed from the ventral side; showing the 
attachment of the crura to the primary lamellz, the form of the 
jugum, its long, straight, bifurcate stem and the shape of the spiral 
cones. X 2. 
St. Louis group. Spergen Hill, Indiana. 
EuMETRIA VERA, var. costar, Hall. 
Fig. 5. A dorsal view of a specimen from which the shell has partially exfo- 
liated exposing the muscular impression on the brachial valve. 
Chester limestone. Chester, Illinois. 
Fig. 11. The interior of the umbonal portion of the brachial valve; showing 
the posterior horns {of the hinge-plate, the posterior, the concave 
median plate and the elongate, narrow dental sockets. X 3. 
Chester limestone. Crittenden county, Kentucky. 
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