PLATE Vb. 



(Figures 3, t, 8, 15 -.n, 27-3'J, by K. P. WmxriELu; 9, i2--2ii, by E. Liuio-xs; 10-11, by J C. McCo.nnell.) 



Legend. A- Deltidium. a. Aiiterioi- aiiiiuctor impressions. 



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



t. Teeth. r. Anterior diiluctor impressions. 



b. Sockets. r'. Posterior didnctor impressions. 



c. Crura. o. 0\'arian marking's, 

 s. Septum. V. Vascular markings, 

 p. Pedicle muscle. 



PLATYSTEOPHIA, King. 



Page -100. 



OUTHIS BIFORATA, Sclllotlicim, Viir. LYNX, vou Eicliwiilcl. 



Fig-. 1. A cardinal view of an average individual ; showiTig the area and deUhyrium 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 quadripartite impi-ession af the adiluctor muscles. 

 Fig. 4. The interior of a lai-ge pedicle-valve. The apical portion of the shell has been absoi'bed, being 



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



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



I'ian markings. 



Hudson River group. Cincinnati, Ohio. 



Orthis BIFORATA, Sclilotheiiii, v:ir. LATicosTA, Meek. 



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

 Fig. 8. The intei'ior of a brai-hial valve. 



Fig. 9. An enlai-gement of the delthyrial portion of the brachial valve. The obsolescent character of 

 the cardinal process is probably due, in jjart, to reabsorption. 

 Hudson Rivei' group. Cincinnati, Ohio. 



Orthis biforata, Sclilothcim. 



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

 very i-arely retained (ami almost never visible in ordinary specimens). X 3. 

 Trenton limestone. Trenton Falls, N. Y. 

 For further illustration of Plattsthophia, see Davidson, Silurian Brachiopoda, pi. xxxviii, tigs. H- 

 2.5 ; Palaeontology of Ohio, Volume I, plate x. 



BILOBITES, LixNE. 



Page 201. 



Orthis biloba, Liiine. 



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 view^s 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 intei-ior of the brachial valve ; showing the cardinal pi-ocess, the great ci'ura, large muscular 

 area, and the i:)ectinated surfaces of marginal contact. X 5. 

 Lower Helderberg group. Near Clarksville. N. Y. 



