PLATE XL— Continued. 



Whitfieldella oylindrica, Hall. 



Kig8. 16, 17. Ventral and pi-ofile views of a large individual. 



Figr. 18. A preparation of the brachidium ; showing the mode of attachment of the spirals and the form 



of the loop, (c.) 

 Fig. 19. A similar preparation ; showing the form of the spirals when exposed by the removal of the 



brachial valve, (c ) 

 Fig. 20. The internal cast of a pedicle-valve j showing the de<>p impression of the diiluctor scai-s. 

 Fig, 21. The internal cast of a t>rachial valve ; showin!.' the impressions of the crural plates and short 



median septum. The anterior portions of this shell are concealed by the matrix. 



Fig. 22. The exterior of a normal example ; showing the high shouldered umbones and inconspicuous 



beak. 



Niagara group. Hillsboro, Ohio. 



Genus HYATTELLA, gen. nov. 



Page 61. 



Hyattella conoesta, Coiuad. 



Fig. 23. The internal cast of a pedicle-valve ; showing the impressions of the pedicle-cavity and the muscu- 

 lar area. X 2. 

 Fig. 24. A cardinal view of the same sjiecimen ; showing the impression of the dental lamellae and of the 

 divided hinge-plate. X 2. 



Clinton group. ReyndU's Basin, N. T. 

 Fig. 25. Exterior of a i-ather large specimen : showing the trilobation of the exterior which is frequently 

 more developed than in this instance ; also the tine concentric lineation of the surface. X 2. 

 Clinton group. Lockport, N. Y 

 Fig. 26. A restoration of a brachidium, made from transverse sections of silicitied specimens, (c ) 



Clinton group. ReynaWa Basin, N. Y. 

 Fig. 27. The cardinal portion of a bi-achial valve ; showing the sti-ucture of the hinge-plate, its narrow 



median division, and the bases of the crura. X 5. 

 Fig. 28. The same specimen viewed in profile from the front ; showing the conspicuous elevation of the 

 lateral divisions. X 5* 



Clinton group. Lockport, N. Y. 



Hyattella Junia, Billings. 



Figs. 29-31. Three views of a normal individual ; showing the strong lobation of the surface and the tine 

 concentric lineation. X 2. 



Middle Silurian. Cape East, Anticosti. 



