PLATE IX— Continued. 



Steophomena planumbona, Hall, = StropJiomena rug/osa, Ratiiiesque (de 



Bltiiiiville). 

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

 Fig. 16. The interior of a brachial valve. On account of the great convexity [of this valve, the cardinal 



process is projected upward at an unusual angle. 

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

 Hudson River group. Lebanon, Ohio. 

 For other illustrations, see PalEeontology of New York, Vol. I, plate xxxi b, fig. 4 ; Palaeontology 

 of Ohio, pi. vi, fig. 3 ; and this volume, plate ix A. 



Steophomena subtenta, Conrad. 



Fig. 18. The exterior of a brachial valve; showing the oblique wrinkling of the shell about the cardinal 

 extremities, as frequently observed in /S". filitexta. 

 Trenton limestone. Wisconsin. 



Steophomena planoconvexa, Hall. 



Fig. 1.9. A view of the brachial valve ; showing the general external characters of the species. 

 Fig. 20. A i>rofile ; showing the reversed convexity of the shell. 

 Hudson River group. Cincinnati, Ohio. 

 Foi- other illustrations, see PalEeontology of Ohio, Vol. I, plate vi, fig. 2. 



Genus OETHOTHETES, Pandee. 



Page 253. 



Oethothetes subplana, Conrad. 

 (See Plate IXa, fig. 19.) 

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



Niagara gi'oup. Lockport, N. T. 

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



valve. 

 Fig. 23. The interior of the brachial valve ; sho^ving the character of the cardinal process, the short, ab- 

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

 on this valve. 

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

 Niagara group. Waldron, Indiana. 

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

 port on the New York State Museum, plate xxi. 



Oethothetes Woolwoethana, Hall. 



Fig. 25. A view of the brachial valve ; showing the general form of the shell and the ai-ea and deltidium 



of the opposite valve. 

 Fig. 26. A profile of the same specimen. 

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



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

 Fig. 28. A postei'ior view of the same parts ; showing the lobation of each branch of the cardinal process, 



and the additional lobes on each side between the pi'ocess and the dental sockets, thus making 



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

 Fig. 29. Anothei' anterior view of the cardinal process, in which the lobes are rather more prominent and 



the crural bases less pronounced. X 3. 

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

 Lower Helderberg group. Near Clarksville, N. Y. 



Oethothetes Chemongensis, Conrad, var. Pandora, Billings. 



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

 plate X ; placed upon this plate by mistake. 



