Fig. 10. The opposite side of the same specimen. The imperfection of the 

 valve in the umbonal region has rendered it impossible to determine with 

 accuracy the generic character of the species, x 2. 

 Trenton limestone. Minneapolis, Minnesota. 



Obbiculoidea numulus, Hall. 

 Page 333. 

 Fig. 11. The exterior of a pedicle-valve. 

 Lower Helderberg group (Waterlime) . Marshall, N. Y. 



Ohbiculoidea (Schizotketa) ovalib, Hall. 



Page 332. 



Fig. 12. View of the pedicle-valve; showing the short foraminal groove, x 3. 



Fig. 13. Profile of the same specimen; showing the valves in juxtaposition. 

 X 3. 

 Trenton limestone . Middleville, N. Y. 



Obbiculoidea Heezebi, Hall. 

 Page 333. 

 Fig. 14. The exterior of a pedicle-valve, x 1.5. 

 Cuyahoga shale . Berea, Ohio . 



Fig. 15. An internal cast of a brachial valve ; showing the impressions of two 



strong, diverging vascular sinuses (?) and finer markings about the 



margins, x 1.5. 

 Cuyahoga shales . Newark, Ohio . 

 Fig. 16. The internal pedicle-area, having the lateral pedicle callosities 



coalesced, leaving the foramen open but otherwise concealing the structure 



of the area, x 3. 

 Fig. 17. A similar structure, x 3. 

 Fig. 18. The interior of the apical portion of the brachial valve; showing the 



small median septum, extending forward from the apex, x 3. 



Fig. 19. The internal pedicle-area, in which the lateral callosities have not 

 fully coalesced . x 3 . 

 Cuyahoga shales. Berea, Ohio. 



Fig. 20, A similar structure, the lateral callosities being somewhat more com- 

 pletely united . x 3 . 

 Cuyahoga shales . Baconshery, Ohio. 



48 37r 



