PLATK IX— Contiuueil. 



Stkophomena planumbona. UiiW. ^ S(ro2)komenu rilgosa, Rafinesquc (de 

 • Bltiiuville). 



Fig. 15. A view of the brachial valve ; showing- the usual foiiu and proportions of the species. 

 Fig. It). The interior of a brachial valve. On account of the great convexity [of this valve, the cardinal 

 process is projected ujiward at an unusual angle. 



Fig. 17. The interior of a pedicle-valve ; showing the usual character of the nmscniar markings. 

 Hudson River group. Lebanon, Ohio. 



For other illustrations, see Palaeontology of New York, Vol. I, plate x.\xi b, tig. 4 ; Pahwmtology 

 of Ohio, pi. vi, tig. 3 ; and this volume, plate ix a. 



Strophomena subtenta, Cuarud. 



Fig. 18. The extei-ior of a bi-achial valve; showing the oblicjue wrinkling of the shell about the cardinal 

 exti'emities, as frequently observed in /S. filitezta. 

 Trenton limestone. Wisconsin. 



Strophomena planoconvexa, Hall. 



Fig. 19. A view of the brachial valve; showing the general external characters of the species. 

 Fig. 20. A profile ; showing the reversed convexity of the shell. 

 Hudson River group. Cinci?i?iati, Ohio. 

 For other illustrations, see Palaeontology of Ohio, Vol. I, plate vi, tig. 2. 



Genus ORTHOTHETES, Pander. 



Page 253. 



Orthothetes subplana, Coinad. 



(See Plate IXa, fig. 19.) 

 Fig. 21. The interior of a pedicle-valve ; showing the muscular impressions. 



Niagara group. Loekport, N. Y. 

 Fig. 22. A view of the brachial valve of an old example ; showing the area and deltidiuni of the opposite 



valve. 

 Fig. 23. The inteiior of the brachial valve ; showing the character of the cardinal process, the short, ab- 

 ruptly terminating crural jilates, and the edge of the deltidium which is very highly developed 

 on this valve. 

 Fig. 24. A profile ; showing the subequally convex valves. 

 Ni.agara group. Waldron, Indiana. 

 For other illustrations, see Palseontology of New York, Vol. II, plate liii ; and Twenty-eighth Re- 

 port en the New York State Museum, plate xxi. 



Orthothetes Woolworthana, Hall. 



Fig. 25. A view of the bi-achial valve ; showing the genei-al form of the shell and the area and deltidium 



of the opposite valve. 

 Fig. 26. A profile of the same specimen. 

 Fig. 27. An enlargement of the cardinal process ; showing its bilobed character from this point of view, 



and the high crural plates ending abruptly at the crural bases. X 3. 

 Fig. 28. A posterior view of the same parts ; showing the lobation of each branch of the cardinal jirocess, 



and the additional lobes on each side between the process and the dental socket.s, thus making 



the posterior face of the divaricating process appear six-lobed. X 3. 

 Fig. 29. Another anterior view of the cardinal process, in wbicb the lobes are rather more prominent and 



the ci-ural bases less pronounced. X 3. 

 Pig. 31. The interior of a pedicle-valve ; showing the deltidium and muscular impressions. 

 Lower Helderberg group. Near Clarksville, N. T. 



Orthothetes Chemungensis, Comad, var. Pandora, Billings. 



Fig. 30. An enlargement of the hinge area, cardinal process, crural plates, etc., of the specimen, tig. 3, 

 plate X ; placed upon this plate by mistake. 



