I'LATK VlA-Conlinued. 



OuTHis Thie.Mii, White. 

 Fig. 14. The interior of the iieiiicle-valve. X 3. 



Fi"-. 15. The interior of a brachial valve which retains the ba,?es of the crura at the extremities of the crural 

 plates. X H. 



Burlington limestone (arenaceous beds). BurVmrjton. Iowa. 

 The specimen referi-ed to this species, with doubt, in Pala;onlology of New York, Volume IV, p. 

 &'i, plate viii, tig. 2, is not 0. T/iinnu, and will require a different leference. 



Okthi.s ilissouitiENsis,* Swullow. 



Fi^s. 16, 17. Interior.s of the brachial and pedicle-valves. The asymmetry of the muscular area is an ac- 

 cidental inisr('|)resentatinn. 



Choteau limestone. Pike amnty, Missouri. 



OrTHIS DUBIA, Hall. 

 Figs. IS, 22. Views of opposite si<tes of the same specimen ; showing the peculiar form of the shell. X 2. 



St. Louis gi'oup. Lebanon, Kentiiclty. 

 Fi". 19. The interior of a pedicle-valve ; showing the large delthyriura and strong teeth with the absence 

 of a cardinal ai'ea. X 2. 

 The limitations of the muscular area are shown, but its sub<livisions are not pi'eserved. 

 St. L(mis group. Lancsville. Iiidiana. 

 Fig. 20. Intei-ior of the pedicle-valve, retaining moie distinctly the subdivisions of the muscular area. X 2. 



Chester limestone. Litclifitld, 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. Lanctville, IndiaTia. 



SCHIZOPHORIA, King. 



Pa2;e 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 scai-s. 

 Clinton group. Reynale's Basin, N. Y. 



Orthis multistriata, Hall. 

 Fig. 2.5. An internal cast of the brachial valve of one of the original specimens; showing the subdivision 

 of the muscular area and the divei-ging vascular sinuses. 



Lower Helderberg grou)!. Near Clarksville, iV. T. 

 For further illustration, see Palseontology of New York, Volume III, plate xv, fig. 2. 



Orthis uipressa, Hall. 



(See Plate VI, tig. 31.) 

 Figs. 26, 27. Two internal casts of the brachi.al valve, which ret.ain with unusual distinctness the muscular, 

 vascular and ovarian markings, and also the iraiiression of the multipartite cardinal process. 

 Chemung group. LawrencevWe. Pennsyivajiia. 

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



Orthis Iowensis, Hall. 



Fig. 29. The interior of a pedicle-valve ; showing the mu.scular ai-ea with a strongly thickened and elevated 

 centi'al addiictur im|U'ession. 



Chemung group, ijjae Creek, Io\Ba. 

 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 gi-oup. High Point, N. T. 

 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 bi'achial 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 [irocess shows its subdivision on the po.sterior face. 

 Chemung grou|>. Hir//i Point, N. Y. 

 Compare figures iia-k, Orthis Tallimisis, PaUeontology of New York, Volume IV, plate 7. 



Tlii.s name was preoccupied b,v Orthis Missouriensis, Sluunard ; Reports 1 and II of the Geological Survey of Missouri, 



law 



rcstv 



• Tlii.s name was preoccupied b,v Orthis Missouriensis, Sliumard ; Reports 1 and II of the Geological Survey of Missouri, 

 , part ii, pajre 20.i, plate C, Bgs. 9 a, b. That species, if belonpinp to tlie ORTHWJi, should be placed under Orthis as 

 ricted, or under Uixoktuis, thus leavins Orthis Missouriensis of Swallow under the genus Khipodomelh 

 t The species of OitTUIS= ScHizoiMIoiiiA, de.scribcd as O propinqua, O Tnlliensis, O ivipressa. Iowensis and 

 0. Macfarlanii, present so many features in common that farlhcr stutl\- aLid conip.irison should be Riven them to determine 

 the actual value of the characters on which the specific distinction has been bjised, and whether these differences coincide 

 with their geological relations. 



