PLATE XLIX. 



(Figures 1, 4, 7, 8, 11, 15, 21, 36-38, 46 by E. Emmons; 2, 3, 5, 6, 9, 10, 22-38, J9-42 by K. P. Whitfield; 13, 14, «-*6, 



47 by G. B. Simpson.) 



Legend : c. Craral lobes. t. Teeth. 



c'. Posterior portion. dt. Delthyrial tube, 



dp. Coalesced deltidial plates. 



Genus HINDELLA, Davidson. 



Pago 63. 

 See Plate 41. 

 HiNDELLA Pkinstana, Billings. 

 Fig. 1. A preparation exposing ihe sti-iicture of the brachidium by removal of a portion of the pedicle- 

 valve ; showing the anterior position of the loop, its obli(iue direction, long lateral branches and 

 short terminal process. The spiral cones are represented as having their upper halves 

 removed. X 3. (c.) 



Middle Silurian. Junction Cliff, Anticosti. 



Genus TREMATOSPIRA, Hall. 



Page l-'4. 



Trematospira camura, Hall. 



Fig. 2. A dorsal view of the exterior of conjoined valves. 

 Fig. 3. A ventral view of a similar, somewhat larger specimen. 



Fig. 4. A view of a preparation showing by ti'ansliicence the structure of the brachidium. X 3. (c.) 

 Niagara group. Lockport, M. Y. 



Trematospira perforata, Hall. 



Figs. 5, 6. Dorsal and ventral views of a typical indivi<lual, showing the character of the exterior. 

 Lower Helderberg group (Shaly limestone). Tke Helderbergs, iV. Y. 



Trematospira Hippolyte, Billings. 



Figs. 7, 8. Dorsal and proiile views of the oiiginal specimen. 



Lower Helderberg group. Square Lake, Maine. 



Trematospira multistriata, Hall. 



Figs. 9, 10. Doi-sal and ventral views of the exterior of a normal example. 



Fig. 11. A preparation showing one of the spii-al cones, the form and position of the loop and the mode of 

 attachment of the primaiy lamellae and crura, (c.) 



Fig. 12. The central cardinal portion of the pedicle-valve, viewed from the apex ; showing the foramen, 

 teeth and coalesced concave deltidial plates. The median line of union of the latter is retained 

 on the specimen, but is obscured in the lithograph. 



Fig. 13. The hinge-plate viewed from its upper surface, showing its deep meiiian excavation, the promi- 

 nence of the lateral lobes and their division into anterior and posterior processes. X 3. 



Fig. 14. Another specimen of the hinge-plate viewed from the apex of the valve ; showing the elevation of 

 the post-lateral lobes, the formation of a small median callosity, the constriction at the base of 

 the process and the striated basal callosity, the lateral portions of which form the socket-walls. 

 l"he apex of the valve, lying without and below this area, should have been more distinctly 

 represented, the plications diverging from this point. X 3. 



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



Trematospira dubia, Billings. 



Figs. 15, 16. Dorsal and cardinal views cjf the oiifjinal specimen. 



Lower Helderberg group. Square Lake, Maine. 



Trematospira simplex, Hall. 



Fiy. 17. A dorsal view of a normal example ; shuwing the external characters. X 2. 



Fig. 18. An enlargement of the surface of the fame specimen ; showing the pustules of the outer 

 laminK. X 5. 



Lower Helderberg group. Decatur county, Tennessee. 



Trematospira costata, Hall. 



Fig^. 19, 20. Dorsal and ventral views of a vei'y large and finely developed individual; showing the trans- 

 vei-se form, the character of the plication and concentiic lineation. 



Lower Helderbei'g group (Shaly limestone). The Helderbergs, N. Y, 



