PLATE VI a—C ontinued. 
Orthis Thiemii, White. 
Fig. 14. The interior of the pedicle-valve. X 3. 
Fig. 15. The interior of a brachial valve which retains the bases of the crura at_the extremities of the crural 
plates. X 3. 
Burlington limestone (arenaceous beds). Burlington, Iowa. 
The specimen referred to this species, with doubt, in Palaeontology of New York, Volume IV, p. 
63, plate viii, fig. 2, is hot 0. Thiemii, and will require a different reference. 
Orthis Missouriensis,* Swallow. 
Figs. 16, 17. Interiors of the brachial and pedicle-valves. The asymmetry of the muscular area is an ac¬ 
cidental misrepresentation. 
Choteau limestone. Pike county, Missouri. 
Orthis dubia, Hall. 
Figs. 18, 22. Views of opposite sides of the same specimen; showing the peculiar form of the shell. X 2. 
St. Louis group. Lebanon, Kentucky. 
Fig. 19. The interior of a pedicle-valve ; showing the large delthyrium and strong teeth with the absence 
of a cardinal area. X 2. 
The limitations of the muscular area are shown, but its subdivisions are not preserved. 
St. Louis group. Lanesville, Indiana. 
Fig. 20. Interior of the pedicle-valve, retaining more distinctly the subdivisions of the muscular area. X 2. 
Chester limestone. Litchfield, Kentucky. 
Fig. 21. The interior of a brachial valve ; showing the greatly thickened and elevated hinge-plate bearing 
the cardinal process and crural plates. X 2. 
St. Louis group. Lanesville, Indiana. 
SCHIZOPHORIA, King. 
Page 211. 
Orthis senectus, sp. nov. 
Fig. 23. The exterior of a pedicle-valve ; showing its depression over the pallial region. 
Fig. 24. An internal cast of the pedicle-valve ; showing the diductor and adductor scars. 
Clinton group. Heynale's Basin, N. Y. 
Orthis multistriata, Hull. 
Fig. 25. An internal cast of the brachial valve of one of the original specimens; showing the subdivision 
of the muscular area and the diverging vascular sinuses. 
Lower Helderberg group. Near Clarksville, N. Y. 
For further illustration, see Palaeontology of New York, Volume III, plate xv, fig. 2. 
Orthis impressa, Hall. 
(See Plate VI, fig. 31.) 
Figs. 26, 27. Two internal casts of the brachial valve, which retain with unusual distinctness the muscular, 
vascular and ovarian markings, and also the impression of the multipartite cardinal process. 
Chemung group. Lawrenceville, Pennsylvania. 
For further illustration, see Palaeontology of New York, Volume IV, plate viii, figs. 11-19. 
Orthis Iowensis, Hall. 
Fig. 29. The interior of a pedicle-valve ; showing the muscular area with a strongly thickened and elevated 
central adductor impression. 
Chemung group. Lime Creek, Iowa. 
See Geology of Iowa, Volume I, part ii, plate ii, figs. 4 a-i. 1858. 
Orthis Macfarlanii, Meek.f 
Fig. 28. The interior of a portion of the brachial valve, retaining at ( x ) the accessory adductor impressions. 
Chemung group. High Point, N. Y. 
Fig. 30 Posterior view of a specimen ; showing the great disparity in the convexity of the two valves, the 
lower being the brachial valve. 
Fig. 31. Profile of another individual; showing the gibbosity of the brachial valve. 
Chemung group. Howard, N. Y. 
Fig. 32. An internal cast of a large brachial valve in which the muscular impressions are unsymmetrically 
developed. The cast of the cardinal process shows its subdivision on the posterior face. 
Chemung group. High Point, N. Y. 
Compare figures 5 a-k, Orthis Tulliensis, Palaeontology of New York, Volume IV, plate 7. 
* This name was preoccupied by Orthis Missouriensis , Sliumard ; Reports 1 and II of the Geological Survey of Missouri, 
1855, part ii, page 205, plate c, tigs. 9 a, b. That species, if belonging to the Ortbidje , should be placed under Orthis as 
restricted, or under Dinorthis, thus leaving Orthis Missouriensis of Swallow under the genus Rhipodomella 
t The species of Orthis =: Schizophoiua, described as 0 propingua, 0. Tulliensis, 0 impressa, 0 Iowensis and 
0. Macfarlanii, present so many features in common that farther study and comparison should be given them to determine 
the actual value of the characters on which the speciflc distinction has been based, and whether these differences coincide 
with their geological relations. 
