PLATE XLIX. 



(Figures 1, 4, 7, 8, U, 15, '21, ;i6-3S, 46 by E. EMMONS; 2, 3, fi, G, 9, 10, 22-38, 89-42 by K, P. Whitfield; 13, 14, 43-45, 



47 by G. B. SIMPSON.) 



Legend : k. Crural lobes. t. Teeth. 



c'. Posterior portion. dt. Deltliyrial tube, 



dp. Coalesced deltidial plates. 



Genus HINDELLA, Davidson. 



l^a^^e 63. 



See Plate 41. 



IIlNDELLA PrINSTANA, BillillgS. 



Fig. 1. A pi-eparation exposing ihe strnctnre of the brachidium by lemoval of a portion of the pedicle- 

 valve ; showing the antei'ior position of the loop, its oblique direction, long lateral branches and 

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

 removed. X 3. (c.) 



Middle Silurian. Jwiction Cliff, Aiiticosti. 



Genus TREMATOSPIRA, Hall. 



Page 124. 

 Trematospiea CAMURA, Hclll. 

 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 preiiaration showing by translucence the structure of the brachidium. X 3. (c. ) 

 Niagara group. Locliport, N. Y. 



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 Helderhergs, N. Y. 



Trematospira Hippolyte, Billin<>-.s. 



Figs. 7, 8. Dorsal and protile views of the ojiginal sperimen. 



Lower Heldei-berg group. Square Lake, Maine. 



Trematospira multistriata. Hall. 



Figs. 9, 10. Dorsal and ventral views of the exierior of a normal example. 



Fig. II. A prepai'ation showing one of the spiral cones, the form and position of the loop and the mode of 

 attachment <if the pi'imary lamella? and crura, (c ) 



Fig. 12. The centi-al cardinal portion of the pedicle-valve, viewed fi'oin the apex ; showing the foramen, 

 teeth and coalesced concave deltidial plates- Tlie 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 meilian callosity, the constriction at the base of 

 the process .and the striated 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 oiij;inal specimen. 



Lower Helderberg group. /Square Lake, Maine. 



Trematospiiia simplex, Hall. 



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 

 lamina. X S. 



Lower Helderbei-g group. Decatur county, Tennessee. 



Trematospira costata, Hall. 



Figs. 19, 20. Doi'sal and ventral views of a very large and tinelj developed individual; showing the trans- 

 verse form, the character of the plication ami concentric lineation. 



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



