PLATE XLIX. 
(Figures 1, 4, 7, 8, 11, 15, 21, 36-38, 46 by E. Emmons; 2, 3, 5, 6, 9,10, 22-35, 39-42 by K, P. Whitfield; 13,14, 43-45, 
47 by G. B. SIMPSON.) 
Legend: c. Crural lobes. t. Teeth. 
of. Posterior portion. dt. Delthyrial tube, 
dp. Coalesced deltidial plates. 
Genus HINDELLA, Davidson. 
Page 63. 
See Plate 41. 
IIiNDELLA PrINSTANA, BillillgS. 
Fig. 1. A preparation exposing the structure of the brachidium by removal of a portion of the pedicle- 
valve ; showing the anterior position of the loop, its obli(Xue 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 124. 
Trematospira camera, 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 translucence the structure of the brachidium. X 3. (c.) 
Niagara group. Lockport, N. T. 
Trematospira perforata. Hall. 
Figs. 5, 6. Dorsal and ventral views of a typical individual, showing- the character of the exterior. 
Lower Helderbei-g group (Shaly limestone). The Helderhei-gs, N. Y. 
Trematospira EIippolyte, Billings. 
Figs. 7, 8. Dorsal and profile views of the original specimen. 
Lowei- Heldei-berg group. Square Lake, Maine. 
Trematospira multistriata. Hall. 
Figs. 9, 10. Dorsal and ventral views of the exterior of a noi-mal example. 
Fig. 11. A preparation showing one of the spii-al cones, the form and i)osition of the loop and the mode of 
attachment of the primary lamellse and crura, (c.) 
Fig. 12. The central cardinal portion of the jiedicle-valve, viewed from the apex ; showing the foi-amen, 
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 median excavation, the promi¬ 
nence of the lateral lobes and their division into anterior and posterior processes. X 3. 
Pig. 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 sti-iated basal callosity, the lateral portions of which form the socket-walls. 
The 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 Helderhergs, N. Y. 
Trematospira dubia, Billings. 
Figs. 15, 16. Dorsal and cardinal views of the original specimen. 
Lower Helderberg group. Square Lake, Maine. 
Trematospira simplex, Hull. 
Fig. 17. A dorsal view of a normal example; showing the external chai-acters. X 2. 
Fig. 18. An enlargement of the surface of the same specimen; showing the pustules of the outer 
laminae. X 5. 
Lower Helderberg group. Decatur county, Tennessee. 
Trematospira costata, Hall. 
Figs. 19, 20. Dorsal and ventral views of a vei-y lai-ge and finely developed individual; showing the trans¬ 
verse form, the character of the plication and concentric lineation. 
Lower Helderberg group (Shaly limestone). The Helderhergs, N. Y. 
