PLATE IX—Continued. 
Strophomena planumbona, Hull, = Strophomena rugosa , Rafinesque (de 
Blainville). 
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 Palaeontology of New York, Vol. I, plate xxxi b, fig. 4 ; Palaeontology 
of Ohio, pi. vi, fig. 3 ; and this volume, plate ix A. 
Strophomena 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 . 
Strophomena planoconvex a, 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. Cincinnati, Ohio. 
For other illustrations, see Palaeontology of Ohio, Vol. I, plate vi, fig. 2. 
Genus ORTHOTHETES, Pander. 
Page 253. 
Orthothetes subplana, Conrad. 
(See Plate IXa, fig. 19.) 
Fig. 21. The interior of a pedicle-valve ; showing the muscular impressions. 
Niagara group. Lockport, IV. Y. 
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; showing 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 Palaeontology of New York, Vol. II, plate liii; and Twenty-eighth Re¬ 
port on the New York State Museum, plate xxi. 
Orthothetes Woolworthana, Hall. 
A view of the brachial valve ; showing the general form of the shell and the area and deltidium 
of the opposite valve. 
A profile of the same specimen. 
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. 
A posterior view of the same parts ; showing the lobation of each branch of the cardinal process, 
and the additional lobes on each side between the process and the dental sockets, thus making 
the posterior face of the divaricating process appear six-lobed. X 3. 
Another anterior view of the cardinal process, in which the lobes are rather more prominent and 
the Crural bases less pronounced. X 3. 
The interior of a pedicle-valve; showing the deltidium and muscular impressions. 
Lower Helderberg group. Near Clarksville, N. Y. 
Orthothetes Chemungensis, 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. 
Fig. 25. 
Fig. 26. 
Fig. 27. 
Fig. 28. 
Fig. 29. 
Fig. 31. 
