Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
aelilts 
12, 
13. 
14, 
15. 
17. 
16, 
. Ventral view of a mature individual from the same locality; showing 
the extensions of the concentric lamella. 
Niagara group. Waldron, Indiana. 
. Dorsal view of a finely plicate shell. 
10. 
The interior of a pedicle-valve; showing the broad pedicle-cavity, 
widely separated teeth, pedicle, adductor and diductor muscular 
scars, ovarian markings and crenulated margins. 
The interior of a brachial valve; showing the structure of the hinge- 
plate, dental sockets and muscular scars. 
Hamilton group. Western New York. 
The cardinal portion of the brachial valve enlarged; showing the 
reduced and completely divided hinge-plate, and the broad dental 
sockets traversed by a crenulated median ridge. X 3. 
Hamilton group. Clarke county, Indiana. 
A preparation exposing, by the removal of the brachial valve, the 
brachidium of a large individual. The spiral cones have their 
bases parallel to the surface of the pedicle-valve and their apices 
directed upward and inward into the cavity of the convex brachial 
valve. The figure shows the laterally appressed form of the cones, 
the great width and anterior extension of the primary lamelle, the 
attachment of the latter to the crura and the discrete, recurved 
branches of the jugum. 
Chemung group. Haskinsville, N. Y. 
ATrRYPA spinosa, Hall. 
The exterior of the pedicle-valve ; showing the -extension of the con- 
centric lamella into well defined spinules. 
Hamilton group. Moscow, N. Y. 
Arrypa aspERA, Schlotheim, var. occipenTatts, Hall. 
A preparation of the brachidium exposed by the removal of the 
pedicle-valve. 
Profile view of the exterior; showing the gibbosity of the brachial 
valve and the coarse plications. 
Upper Devonian. Independence, Iowa. 
Atrypa HystrRix, Hall. 
The exterior of a pedicle-valve, with coarse ribs, strong concentric 
lamellze and stout long marginal spines. 
Chemung group. Near Bath, N. Y, 
124 237 
