PLATE XL VIII. 



(Pigs. 1-3, 6, 10, U, 21-21, 26-29, 33, 34 by E. Emmons; 4, 6,',7-9 by F. B. MEEK; 12-20, 25, 30-32 by E. P. Whitfield.) 



Legend : D. Coalesced deltidial plates. r. Deductors. 



t. Teeth. c. Crura. 



8. Median septum. hp. Hinge-plate, 



a. idductoi-8. ub. Umbonal blades. 

 a'. Anterior adductors. 1. Stem of loop. 



Genus NUCLEOSPIRA, Hall. 



Page 142. 



NucLEOSPiRA PisuM, Sowerby. 



Fig. 1. A dorsal view; showing the fine surface spines. X 2. 

 Wenlock shale. England. 



NuCLEOSPIRA VENTRICOSA, Hall. 



Fig. 2. A dorsal view of conjoined valves which retain the epidermal spines over a portion of the surface. 

 X 2. 



Fig. 3. A profile view of a comparatively large individual, denuded of its spines ; showing the usual con- 

 vexity of the valves. 



Fig. 4. A profile view of a brachial valve ; showing the crural bases and the recurved hinge-plate 

 extending backward beyond the apex of the valve. 



Fig. 6. The interior of a brachial valve with the umbonal portion of the pedicle-valve adhering, viewed 

 from in front ; showing the elevation and lobation of the hinge-plate, and the median septum. 



Fig. 6. A preparation, showing the broad umbonal blades of the primary lamellse, their attachment to the 

 crura, and also the lateral branches of the loop, the upright stem being broken off. X 3. 



Kg. 18. The interior of a pedicle-valve ; showing the concave coalesced deltidial plates and the median 

 septum. 



Lower Helderberg group (Shaly limestone). The Helderbergs, N. Y. 



NuCLEOSPIRA CONCENTRICA, Hilll. 

 Pig. 7. The exterior of a pedicle-valve ; showing the shai-p concentric giowth-Iines. 

 Lower Helderberg group. Decatur county, Tennessee. 



NuCLEOSPIRA ELEGANS, Hall. 

 Fig. 8. A dorsal view of conjoined valves ; showing the transverse form of the shell and the low median 



sinus on the brachial valve. 

 Fig. 9. A profile view of the same specimen. 



Lower Helderberg group. Cherry Valley, N. Y. 

 Fig. 10. A preparation exposing, by the partial removal of the pedicle-valve, the structure of the brachi- 

 dium. In the umbonal region the crura and umbonal blades are exposed, and at (I) is the 

 projecting upright stem of the loop. All of the lamellae are slightly encrusted with a silicions 

 deposit. X 2. 

 Fig. 11. A profile of the same specimen ; showing one of the cones and the projecting extremity of the 

 loop. X 2. (c.) 



Lower Helderberg group (Shaly limestone). Schoharie, N. T. 



NuCLEOSPIRA CONCINNA, Hall. 



Pig. 12. A dorsal view of conjoined valves retaining a portion of the spinulose surface. 



Figs. 13-16. Ventral, dorsal, cardinal and profile views of a normal example from which the surface spinules 

 have been lost ; showing the normal subplano-convex contour of the valves and the linear 

 median depression on each. 



Fig. 17. The interior of a pedicle-valve ; showing the concave, coalesced deltidial plates, articulating pro- 

 cesses, adductor and diductor scars. 



