PLATE IV. 



Oethis Panderiana, Hall. 

 Page 338. 

 Figs. 1, 2. Exterior and interior of a pedicle-valve, x 3. 

 Fig. 3. Interior of a brachial valve, x 3. 

 (From the originals of Billings's species . ' ' Orthis orthamhonite^, Pander . " 

 ^^ Point Levis; in the upper part of Limestone No. 2, Quebec group. '^ 



Orthis flabellites, var. spania, Hall. 



Page 339. 



Fig. 4. An internal cast of a pedicle-valve, having the expression of O. flabel- 

 lites, but with scarcely more than one- half the number of plications usual 

 in this species . 

 Niagara dolomites . Near Milwaukee, Wisconsin. 



Orthis (?) gltpta, Hall. 

 Page 338. 



Fig. 5. A partial internal cast of a pedicle- valve ; showing the outline of the 

 shell, its surface ornamentation and the form of the muscular impression. 

 Fig. 6. A similarly preserved shell with but a single series of radial plica- 

 tions and showing the peculiar reticulating surface sculpture, x 2. 

 Niagara dolomites . Near Milv^aukee, Wisconsin. 



Orthis (Pl^siomys) loricula, Hall. 

 Page 339. 

 Fig . 7 . The exterior of a pedicle-valve . 

 Fig. 8. The interior of a brachial valve. 



Fig. 9, The interior of a pedicle- val ve ; showing the character of the muscular 

 area and ovarian markings . 

 Galena limestone . Fountain, Minnesota . 



O&this (?) Saffordi, Hall. 



Page 340. • 



Figs. 10, 11, 12. Ventral, profile and dorsal views of the exterior, showing the 

 characters of the species. 

 Trenton, horizon. Near Knoxville, Tennessee. ^ 



Orthis (Dalmanella) aecuaeia, Hall. 



Page 340. f 



Figs. 13, 14. Dorsal and profile views of a silicified and partially exfoliated 

 shell. 

 Niagara group . Perry county , Tennessee . 



380 



