PLATE XL— Continued. 



WhITFIELDKLLA CYLINDlilCA, Hilll. 



Figs. 16, 17. Ventral and iirotile views of a large individual. 



Fig. 18. A preparation of the brachidium ; .showing the mode of attachment of the spiials ami the form 



of the loop. (c. ) 

 Fig. 19. A similar preparation ; showing the form of the .spirals when exi)Osed by the removal of the 



brachial valve, (c ) 

 Fig. 20. The internal cast of a pedicle-valve ; thowing the deep impression of the diductor scars. 

 Fig. 21. The internal cast of a brachial valve ; showinu' the irai)]-ession8 of the crui'al plates and short 



median septum. The antei'ior portions of this shell are concealed by the matrix. 



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



beak. 



Niagara group. Hillsboro, Ohio. 



Genus HYATTELLA, gen. nov. 



l"age Ul. 



Hyattella congesta, Coniiid. 



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 lamella? and of the 

 divided hinge-plate. X 2. 



Clinton group. Reynalts 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 fine concentric lineation of the sui'face. X 2. 

 Clinton gi-oup. Lockport, N. Y 

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



Clinton group. Reijnali''s Basin, N. Y. 

 Fi". 27. The cardinal jioition of a bracliial valve ; .showing the sti-ucture of the hinge-plate, il.s narrow 



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

 Fig. 28. The same sjieciraen viewed in profile from the front; showing the consjiicoous elevation of the 

 lateral divisions. X 5. 



Clinton group. Lockport, iV. Y. 



Hyattella Junia, Billings. 



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

 concentric lineation. X 2. 



Middle Silurian. Cape Bast, Anticosti. 



