PLATE LV. 
*1 
V 
y- 
■# 
(Figures 1 by J. M. Clarke; 2, II, 12,15-17 by G. B. Simpson; 3-9,18-21, 23, 26, 27 by R. P. Whitfield; 10, 13,14, 
22, 24, 25 by E. EMMONS.) 
Legend: P. Pedicle passage. 
sr. Ridge in dental sockets. 
p. Pedicle cavity. 
a. Adductor scars. 
dp. Deltidial plates. 
n. Diductor scars. 
■i 
hp. Hinge-plate. 
0 . Ovarian markings. 
' 
c. Crural lobes. 
V. Vascular trunks. 
A- 
b. Dental sockets. 
v'. Secondary vascular sinuses. 
j. 
Genus ATRYPA, Dalman. 
Page 163. 
Atrypa reticularis, Lin lie. 
Fig-. 1. Dorsal view of the youngest individual observed; showing the slight convexity of the brachial 
valve in the umbonal region, its general depression anteriorly, low median sinus, few plications, 
erect beak of pedicle-valve, triangular delthyrium and incipient deltidial plates. X 10. 
Fig. 2. Exterior of the pedicle-valve of a mature individual from the same locality; showing the exten¬ 
sions of the concentric lamellae. 
Niagara group. Waldron,, Indiana. 
Figs. 3, 4. Dorsal and profile views of an elongate, finely plicate and gibbous shell, without strong con¬ 
centric growth lines. 
Lower Helderberg group (Shaly limestone). Near Clarksville, N. Y. 
Figs. 5, 6. Dorsal and profile views of an orbicular, subequally biconvex, finely plicate shell. 
Fig. 7. The interior of a pedicle-valve ; showing the broad pedicle cavity, widely separated teeth, pedicle, 
adductor and diductor muscular scars, ovarian markings and crenulated ante-lateral margins. 
Fig. 8. The interior of a brachial valve ; showing the structure of the hinge-plate, dental sockets and the 
muscular scars. 
Hamilton group. In the soft shales of western New York. 
F'ig. 9. An internal cast of a large pedicle-valve ; showing the impression of the rostral cavity and large 
muscular scars, ovarian markings, vascular trunks and secondary sinuses. 
Corniferous limestone. Le Roy, N. Y. 
Fig. 10. A preparation exposing the brachidium of a lai-ge individual, by the removal of the brachial valve. 
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 
lamellffi, the attachment of the latter to the crura, and the discrete, recurved branches of the 
loop. (c.) 
Chemung group. Haskmsville, N. Y. 
Fig. 11. The cardinal portion of the brachial valve, enlarged ; showing the reduced and completely divided 
hinge-plate, and the broad dental sockets which are-traversed by a crenulated median ridge. X3. 
Fig. 12. A posterior view of the cardinal portion of the pedicle-valve ; showing the elevation of the distant 
teeth, the double grooving and recurvature of their extremities. X 3. 
Figs. 13, 14. Fragments of the spiral lamellse ; showing their fimbriate outer margin. X 10. 
Fig. 15. A portion of the primary lamellae with its attachment to one of the crura. This specimen is viewed 
from -the dorsal side and shows the incurvature of the crus and its union with the outer edge 
of the lamella. X 10. 
Fig. 16. A view of the loop drawn from the venti-al side of the brachidium ; showing the thickened and 
recurved extremities of the lateral branches. X 10. 
Fig. 17. A portion of the primary lamellae and one of the crura, the latter being in a pathologic condition 
which has resulted in hypertrophy of this part. X 10. 
Hamilton group. Clarke county, Indiana. 
