780 CAMBRIAN BRACHIOPODA. 



^ EOOETHIS IDDINGSI (Walcott). 



Plate XCI, figures 3, 3a-b. 



Orthisf remnicha Walcott (in part) [not N. H. WiNCHEif.], 1899, Mon. U. S. Geol. Survey^ vol. 32, pt. 2, pp. 451-452, 

 PL LXII, figs, la and lb (not PL LXI, figs. 3 and 3a, or PL LXII, figs. 1, Ic, and Id). (Specimens now referred 

 to Eoorthis iddingsi were included with E. remnicha when this description was written, two being figured, PL 

 LXII, figs, la and lb. The specimens represented by these two figures are redrawn in this monograph, PL 

 XCII, figs. 3 and 3a, respectively. The specimens represented by PL LXI, figs. 3 and 3a, and PL LXII, figs. 

 1, Ic, and Id belong with EoortkU reinnicha.) 



Orthis (Plectorthis) iddingsi Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, p. 264. (Characterized as below as a new 

 species.) 



General form and convexity mucli like that of some varieties of Eoorthis indianola. Its 

 surface characters also approach those of the more regularly ribbed shells of the latter species. 

 The principal difference between the two species is the less convexity, lower umbo, and lower 

 area of E. iddingsi. The interior of the ventral valve shows a short, well-defined umbonal 

 cavity with a strong vascular sinus on each side of it that extends well forward into the valve. 



The specific name is given in honor of Prof. Joseph P. Iddings. 



Formation and locality. — Upper Cambrian: (302c) Shaly limestone on the south side of the Gallatin Valley, Yellow- 

 stone National Park, Wyoming; and (302d) limestone 200 yards (183 m.) north of the southwest corner sec. 18, T. 28 

 N., R. 113 W., Uinta County; both in Wyoming. 



(71) Limestone in Cold Creek Canyon, Burnet County, Texas. 



EOOETHIS INDIANOLA (Walcott) . 

 Plate XCIV, figures It, lu, 2, 2a-h. 



Orthis (Plectorthis) indianola Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, pp. 264-265. (Described and discussed 



essentially as below, as a new species.) 

 Pectorthis indianola (Walcott), Grabau and Shimer, 1907, North American Index Fossils, vol. 1, pp. 251-252. 



(Described.) 



Shell small, transverse, with the cardinal extremities rounded, angular, and in some speci- 

 mens almost alate. Valves moderately convex, the ventral nearly twice as much so as the 

 dorsal; the length of the hinge line varies from slightly less than the greatest width of the 

 shell to one-fifth greater than the width of the shell across the center, in shells with extended 

 cardinal extremities. 



The ventral valve may or may not have a mesial depression. In some examples the 

 depression is broad and rounded, and in others it is shallow \N\t\\ stronger ribs at each margin; 

 umbo somewhat elevated, and curving over toward the hinge line, beyond which it projects, 

 terminating in a small, incinved beak; dorsal valve considerably less convex than the ventral; 

 beak small and projecting slightly over the hinge line. The median sinus in the dorsal valve 

 varies from a broad, shallow depression to a narrow, rather deep, furrow, that gives a bilobed 

 appearance to the valve (PI. XCIV, fig. 2f) . 



The strength and arrangement of the strong and minor radiating elevated ribs and striae 

 are quite variable. On some shells the ribs or striae are very fine, of nearly equal size, and 

 separated by grooves of about the same width (PI. XCIV, figs. 2f, 2g, and 2h). In other 

 examples every third or more widely separated rib is stronger and elevated above a more 

 or less broad interspace, marked by fine ribs or costse (PI. XCIV, fig. 2). A few of the varia- 

 tions in surface are illustrated. 



Almost nothing is Icnown of the interior of the valves. Below the umbo in a few speci- 

 mens there is a well-marked pseudospondylium that is much like that of E. remnicha. The 

 area of the ventral valve is inclined at an angle of about 65° to the plane of the margin of the 

 valve; it is rather low and broken midway by a strong delthyrium. The area of the dorsal 

 valve is low and inclined weU out over the hinge line. 



Observations. — Eoorthis indianola is almost as variable in its form and surface markings 

 as E. wichitaensis, with which it is associated at a number of localities. It differs from the latter 

 in its bilobed dorsal valve, more strongly incurved umbo and apex of the ventral valve, and 



