PI.ATK \I A— L'ontinucil 



OuTHis TiiiK.Mii, Wliite. 



Fiff. 14. The interior of the pedicle-valve. X 3-  , u i 



Fig. 15. The interior of a brachial viilve which retains the ba.se.s of the cruia at the extremities of the crural 

 plates. X H. _ 



Bui-ling-ton limestone (ai'eiiaceous bails). Burlinffton, Icnm. 

 The si>e(inien referred to this species, with doubt, in Palsiontolog-y of New York, VoUinie IV, p. 

 |j3, plate viii, tig. 2, is not 0. Tliiemii, and will require a diflerent reference. 

 OrTHIS illSSOUUIEXSIS,* Swiillow. 

 Fi"^. 16, 17. Interior.^! of the brachial and pedicle-valve.s. The asymmetry of the mtiscular area is an ac- 

 cidental ini-srejiresentation. 



Choteau limestone. Pike county, Missouri. 



Ortiiis dubia, Hall. 

 Figs. IS, 22. Views of opposite sides of the same specimen ; showing the peculiai- form of the shell. X 2. 



St. Louis gi-oup. 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. Lancsville, Indiana. 

 Fi"-. 20. Inteiior of the pedicle-valve, retaining more distinctly the subdivisions of the muscular area. X 2. 



Chestei- 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 (ilates. X 2. 

 St. Louis group. Lanciville, Indiana. 



SCHIZOPHORIA, King. 



Page 211. 



Orthi.s senectus, .sp. nov. 

 Fi". 23. The exterior of a pedicle-valve ; showing its depression ovei- the pallial region. 

 Fig. 24. An internal cast of the pedicle-valve ; showing the diductor and adductor scars. 

 Clinton gi-oup. Reynale's Basin, N. Y. 



Orthis multistriata, Hall. 

 Fig. 2.1. An internal ca-st of the brachial valve of (me of the original specimens; showing the subdivision 

 of the muscular area and the diverging vascular ."inuses. 



Lower Helderbei-g group. Near Clarksnille, N. Y. 

 For further illu.-itr-ation, see. PaUeontology of New Yoi-k, Volume III, x'late xv, fig. 2. 



Orthi.s impres.sa, Hall. 

 (See Plate VL Hg. 31.) 

 Figs. 26, 27. Two internal oasts of the brachial valve, which lelain with unusual distinctness the muscular, 

 vascular and ovarian mai-kings, and also the imjire.Mon of the multipartite cardinal process. 

 Chemung group. LawrenccviUn. Pev.njiytKania. 

 For further illustration, see PaljEontology of New York, Volume IV, plate viii, figs. 11-19. 



Orthis Iowensis, Hall. 



Fig. 29. The interior of a pedicle-valve ; showing the musciilai' arc^a with a strongly thickened and elevated 

 central adciuctor impression. 



Chemung group Liiae Creek, Iowa. 

 See Geology of Iowa, Vohirae I, part ii, plate ii, figs. 4 a-i. 1S58. 



Orthis Macfarlanii, Meek.f 



Fig. 28. The interior of a portion of the brachial valve, retaining at (x) the accessory adductor iiiipressions. 



Chemung gi-oup. 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 hrac^hial valve. 

 Fig. 31. Profile of another indiviilual ; showing the gibbosity of the brachial valve. 



Chemung group. Howard, N. Y. 

 Fig. 32. An internal ca.st of a large brachial valve in which the muscular impressions are unsymmetrically 

 developed The cast of the carilinal jirocess shows its subdivision on the posterior face. 

 Chemung group. High Point, N. Y. 

 Compare figures ha-k. Orthis TulUensis, Pala;ontology of New York, Volume IV, plate 7. 



• This name was preoccupied by Orthis ^fissouri^msi,•^. shumard ; Reports 1 and 11 of the (i(;oIopical Survey of Missouri, 

 18.Vi, pail ii, pajTO 2u"i, plate c, llgs. fia. I) Thai species, if lulouifiii),' to Mie OiiruiDJi, sliouJd be platc<l under Orthis as 

 rcstricied, or under Uinoktiiis, tlius lea\ iu;< Orthia Missouriensis of .S\\'Ai.LoN\' uinler Ihe genus Kiiiih)I>(»iki,i,a 



1 The species of OUTiilsrr :s<:iiizoiMiiiiiiA, de~irihed a< O propinqua, THiltiensis, O impressa. O Iowensis and 

 O. Mac/arlanii, present so many features in common that I'arlher study and comparison should be given them to determine 

 the actual value of tiie characters on which the speiulio distniction has been based, and whether these difl'erences coincide 

 with their geological relations. 



