PLATE V—Continued. 
Fig. 19. The deltidial portion of the pedicle-valve;'showing the broad deltbyrium and the outline of the 
muscular area which is not sufficiently thickened to obscure the plications of the shell. X 3. 
Fig. 20. The area in the opposite valve; showing.the cardinal process, crural plates and low median 
ridge. X 3. 
Hudson River group. Covington, Kentucky. 
For further illustration, see Palaeontology of Ohio, Volume I, plate viii, fig. 7. 
Orthis dichotoma, Hall. 
0. dichotoma , Hall, = 0. ftssic'dtia."Meek, not Hall. 
The interior of the brachial valve; showing the cardinal process, crural plates and the character 
of the plications. 
Hudson River group. Covington, Kentucky. 
For further illustration, see Palaeontology of Ohio, Volume I, plate viii, fig. 6, under the name of 
0. fissicosta. 
Orthis Ella, Hall. 
An individual viewed from the brachial valve, showing area and foramen of the opposite 
valve. X 2. 
A portion of the interior of the pedicle-valve ; showing the characters of . the cardinal area. X 3. 
Hudson River group. Covington, Kentucky. 
For further illustration, see Palaeontology of Ohio, Volume I, plate viii, fig. 9. 
Orthis Kanilakensis, McChesney. 
Figs. 24, 25. Brachial and profile views of a normal individual. 
Hudson River group. Wilmington, Illinois. 
Orthis Whitfieldi, N. IT. Winchell. 
Fig. 26. The interior of a pedicle-valve ; showing the relatively high area and strong teeth, the character 
of the muscular area, and the low ridges radiating from its anterior margin. 
Hudson River group. /Spring Valley, Minnesota . 
DINORTHIS, nom. nov. 
Page. 195. 
Orthis pectinella (Emmons), Conrad. 
Figs. 27, 28. A view of the pedicle-valve, and profile of a specimen in which the ribs are more subdivided 
toward the margin than is usual in the species. X 2. 
Trenton limestone. Lewis county, New York. 
Fig. 29. The interior of a small pedicle-valve; showing the subquadrate muscular area with the posterior 
and anterior diductor and the adductor scai-s. 
Trenton horizon. St. Paul, Minnesota. 
Figs. 30, 31. A view from the pedicle-valve and the profile of a large individual, showing the strongly ele¬ 
vated, simple ribs. 
Fig. 32. The interior of a pedicle-valve. 11 uvlolfc - i « " • ids • 
Fig. 33. The cardinal portion of a brachial valve. X 2. 
Trenton horizon. Curdsville, Kentucky. 
For further illustration, see Palaeontology of New York, Volume I, plate xxxii, fig. 1'). 
Orthis Sweeneyi, N. H. Winchell. 
Fig. 34. Exterior of the pedicle-valve ; showing the depressed-convex shell. 
Fig. 35. A profile of conjoined valves; in this figure the pedicle-valve as represented is too convex and too 
high at the head. 
Fig. 36. The interior of the brachial valve. 
Trenton horizon St. Paul, Minnesota. 
ORTHIS as restricted. 
Page 102. 
Orthis flabellites, Hall. 
Figs. 37, 38, 39. The exterior of the pedicle and brachial valves and profile of an average specimen. 
Fig. 40. The interior of the pedicle-valve; showing the character of the muscular area. 
Fig. 41. The interior of the brachial valve ; showing the cardinal process, crural plates and quadripartite 
muscular area. 
Niagara group. Lockport, N. Y. 
For further illustration see Palaeontology of New York, Volume II, plate lii, figs. 6, 7. 
Fig. 21. 
Fig. 22. 
Fig. 23. 
