PLATE Vb. 



(Figures 3, 1, 8, 15-21, 27-39, hy R. P. Whitfield; 9, 22-26, by E. EiiiioNS; 10-U, by J C. McConnell.) 



Legend. A- Deltidium. a. Anterior adductor impressions. 



j. Cardinal process. a'. Posterior adductor impressions, 



t. Teeth. r. Anterior diductor impressions. 



b. Sockets. r'. Po.sterior diductor impressions. 



c. Crura. o. Ovarian markings, 

 s. Septum. V. Vascular markings, 

 p. Pedicle muscle. 



PLATYSTEOPHIA, King. 



Page 200. 



Orthis biforata, Schlotheim, var. lynx, vou Eichwald. 



Fig. 1. A cardinal view of an average individual ; showing the area and delthyrium of each valve. (The 

 lines limiting the delthyrium are too strongly defined.) 



Fig-. 2. An exterior of the brachial valve of a smaller specimen. 



Fig. 3. The interior of a brachial valve ; showing the narrow, linear cardinal process, large crural plates 

 and the quadripai'tite impression af the adductor muscles. 



Fig. 4. The interior of a large pedicle-valve. The apical portion of the shell has been absorbed, being 

 the usual condition in old shells of this form, thus exposing the impression of the pedicle-muscle. 

 The specimen also shows tlie compact form of the muscular scars, the vascular trunks and ova- 

 rian markings. 



Hudson Rive]" group. Cincinnati, Ohio. 



Orthis biforata, Schlotheim, vai-. laxicosta, Meek. 



Figs. 5, 6, 7. Profile, brachial and front views; showing the high median fold characterizing this form. 

 Fig. 8. The interior of a brachial valve. 



Fig. 9. An enlargement of the delthyrial portion of the brachial valve. The obsolescent character of 

 the cai-dinal process is probably due, in part, to i-eabsorption. 

 Hudson River group. Cincinnati, Ohio. 



Orthis biforata, Schlotheim. 



Fig. 10. The exterior of the pedicle-valve. The surface is covered with fine granules which, however, are 

 very rarely retained (and almost never visible in ordinary specimens). X 3. 

 Ti-enton limestone. Trenton Falls, N. Y. 

 For further illustration of Platystrophia, see Davidson, Silurian Brachiopoda, pl.xxxviii, figs. 11- 

 25 ; Palseontology of Ohio, Volume I, plate x. 



BILOBITES, LiNNE. 



Page 201. 



Orthis biloba, Liniie. 



Figs. 11, 12, 13, 14. Views ; showing the variation in form in this species. Fig. 14 is of the type described 

 by RiNGDEBERG as 0. acutiloba. X 3. 



Niagara group. Lockport, N. Y. 



Orthis varica, Conrad. 



Figs. 15, 16, 17. Three views of the same specimen. X 2. 



Fig. 18. The interior of the pedicle-valve ; showing the area, delthyrium, teeth and outline of the muscu- 

 lar area. X 4. 



Fig. 19. The interior of the bi-achlal valve ; showing the cardinal process, the great crura, large muscular 

 area, and the pectinated surfaces of marginal contact. X 5. 

 Lower Helderberg group. Near Clarksville. iV. Y. 



