J'l/ATK Vc— Coiitinueti. 



Oiniii.s AHCUARIA, sp. iiov. 



(.See Supplement lur ilesci-iption.) 

 Fiirs. 20, 21. Two views of a siUcified, partially exfoliated shell ; showing' somewhat the contour of 0. de- 

 gantula, but having a more sti-ongly biconvex form. 

 Niagara group. Pi^rrji county, Tennessee. 



Orthis Wisbyensis, Liiidstrom. 



Fig. 22. Profile of the pe(iicle-\alve. 

 Fig. 23. The interior of the same valve. 



Fig. 24. The interior of the brachial valve; showing the cardinal process, crural plates and muscular 

 scars. X 2. 



Upper Siluiian limestone. Islmid of Gotland. 



Orthts subcarinata, Hall. 



Figs. 25, 26, 27, 28. Views of the extei-ior of a normal individual ; showing its form and contour. 

 Fig. 29. The interior of a brachial valve. 

 The interior of a pedicle-valve. 



A natural cast of the intei'ior of the bi'achial valve ; showing tlie limits of the muscular area, the 

 ovarian spaces and the main vascular trunks. 



A similar internal cast of the opposite valve, preserving the ramifications of the vasciilar sinuses, 



and showing also the ovai'ian spaces and muscular scars. 

 Posterior view of the cardinal ai'ea of the brachial valve ; showing the subdivision of the cardinal 



process and the elevation of the crural jilates. 



Lower Helderberg group. Near ClarksvUle, N. Y. 

 For further illustration, see Palaeontology of New York, Volume III, plate xii, tigs. 7-21. 



Orthis perelkgans, Hall. 



Fig. 34. The intei-ior of a bi-achial valve ; showing the ilivei-gent ridges extending from the line of separa- 

 tion between the aiiterioi- and posterior elements of the adductor muscle. 

 Fig. 35. Posterioi' view of the cardinal area of a brachial valve. 



Lower Heldei'berg group. Near Clarksinlle, N. T. 

 For fui'ther illustration, see Paleontology of New Yoi'k, Volume III, plate xiii, tigs. 4-12. 



Orthi.s lenticularis, Vaniixcm [= 0. leiUifnrmi.^, Hull). 

 (See note on page 224.) 

 Figs. 36, 37. Two views of a small individual. 



Corniferous limestone. LeRoy, N. Y. 

 Figs. 38, 39, 40. Views of a larger, more liiconvex specimen. 



Fig. 41. The intei-ior of a pedicle- valve ; showing the character of the muscular area. 

 Coi'iiiferous limestone. Caledonia, N. Y. 



Ortiils Leonensis, Hall. 



Figs. 42, 43. Intei'iors of the brachial and pedicle-valves taken IVom imjn-essions of natural moulds. 

 Chemung group. Cattaraugus county, N. Y. 

 For further illustration, see Paleontology of New Yoi-k, V< lume IV, plate viii, figs. 3-8. 



OUTHIS SUPERSTES, Sp. IIOV. 



(i^ee Supplement for description.) 

 Fig. 44. Proiilo ; showing the convexity of the shell. 

 Fig. 45. A view of the same specimen from the brachial valve. 



Fig. 46. An internal cast of the pedicle-valve; showing traces of the vascular sinvises. 

 Fig. 47. The inteiior of the opposite valve ; retaining similar radiating furi'ows about the muscular area. 

 Chemung group. Howard, N. Y. 



