PLATE LV. 



(Figores 1 by J. M. Clarke; 2, 11, 12, 16-17 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. 



p. Pedicle cavity. 

 dp. Deltidial plates. 

 hp. Hinge-plate. 



c. Crural lobes. 



b. Dental sockets. 



Fig. 



Fig. 



Figs. 

 Kg. 



Fig. 

 Fig. 



Ridge in dental sockets. 

 Adductor scars. 

 Diductor scars. 

 Ovarian markings. 

 Vascular trunks. 

 Secondary vascular sinuses. 



Fig. 



Fig. 



Figs. 



Figs. 

 Fig. 



Fig. 



Fig. 



Genus ATRYFA, Dalman. 



Page 163. 



Atrypa reticularis, Linii6. 



1. Dorsal view of the youngest individual observed ; showing the slight convexity of the brachial 

 valve in the umbonal region, its general depression anteiiorly, low median sinuSi few plications, 

 erect beak of pedicle- valve, triangular delthyrium and incipient deltidial plates. X 10. 



2. Exterior of the pedicle-valve of a mature indiviciual from the same locality ; showing the exten- 

 sions of the concentric lamellae. 



Niagara group. Waldron, Indiana. 



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. 

 5, 6. Dorsal and profile views of an orbicular, subequally Vnconvex, finely plicate shell. 



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. 



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 vxstem New York. 



9. An internal cast of a large pedicle-valve ; showing the impression of the rostral cavity and large 



muscular scars, ovarian mai-kings, vascular trunlis and secondary sinuses. 

 Corniferous limestone. Le Roy, N. Y. 

 Fig. 10. A preparation exposing the brachidium of a large 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 

 lamellae, the attachment of the latter to the crura, and the discrete, recurved branches of the 

 loop. (c.) 



Chemung group. Haskins^rille, N. Y. 

 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. 

 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. 

 13, 14. Fragments of the spiral lamellae ; showing their fimV)riate outer margin. X 10. 

 16. 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. 



16. A view of the loop drawn from the ventral side of the brachidium ; showing the thickened and 

 recurved extremities of the lateral branches. X 10. 



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. 



11. 



12. 



