PLATE XL—Continued. 
WlIITFlELDELLA CYLINDRICA, Hall. 
17. Ventral and profile views of a larg-e individual. 
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 ) 
The internal cast of a pedicle-valve ; showing the deep impression of the diductor scars. 
The internal cast of a brachial valve ; showinc the impi-essions of the crural plates and short 
median septum. The anterioi- 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. 
Figs. 16, 
Fig. 18. 
Fig. 20. 
Fig. 21. 
Genus HYATTELLA, gen. nov. 
Page 61. 
IIyattella congesta, Conrad. 
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 specimen; showing the impression of the dental lamellae and of the 
divided hinge-plate. X 2. 
Clinton gi'oup. Reynale's Basin, N. Y. 
Fig. 25. Exterior of a rather large specimen ; showing the trilobation of the exterior which is frequently 
more developed than in this instance; also the tine concenti-ic lineation of the surface. X 2. 
Clinton group. Lock 2 wrt, iV. Y. 
Fig. 26. A i-estoration of a brachidium, made from ti-ansverse sections of silicified specimens, (c ) 
Clinton group. Beynals’s Basin, N. Y. 
Fig. 27. The cardinal portion of a brachial valve; showing the structure of the hinge-plate, its narrow 
median division, and the bases of the crui’a. X 5. 
Fig. 28. The same specimen viewed in profile from the tVont; showing the consjiicuous elevation of the 
lateral divisions. X 5. 
Clinton group. Lochport, N. Y. 
Hyattella Junia, Billings. 
Figs. 29-31. Three views of a noi-mal individual; showing the strong- lobalion of the surface and the tine 
concentric lineation. X 2. 
Middle Silui-ian. Cape Hast, Anticosti. 
