BRACHIOPODA. 437 



Orthls (Plectorthis) whitfleldl.] 



ORTHIS (PLECTORTHIS) WHITFIELDI N. H. Winckell. 



PLATE XXXIII, FIGS. 8-13. 



1881. Orthis whitfieldi WINCHELL. Ninth Annual Report of the Geological and Natural History 



Survey of Minnesota, p. 115. 



1882. Orthis pectinella WHITFIELD (parti, not EMMONS nor HALL). Geology of Wisconsin, vol. iv, 



p. 259, pi. xn, flg. 8. 

 1892. Pleetorthis whilfieldi HALL. Paleontology of New York, vol. viii, pt. 1, p. 221, pi. v, flg. 26. 



Original description: "Shell semioval, the hinge-line being a little less than, or 

 equal to, the greatest tranverse diameter, the cardinal angles being a little greater 

 than 90, the edge passing in a regular semioval curve through the antero-lateral 

 angles, but sometimes with a very slight inclination in front toward the side of the 

 receiving [ventral] valve. Size varying from nine and a half to fourteen lines in 

 transverse diameter, and from eight to eleven and a half lines in perpendicular 

 diameter, in the larger size the convexity being, between the umboes, six and a 

 half lines. 



"The receiving [ventral] valve has a distinct and full beak and umbo, from 

 which the surface slopes evenly to the margin all round, but having a little flatness 

 at the cardinal angles. The cardinal area is arched, and at its union with the cardinal 

 area of the entering [dorsal] valve forms an angle with it of nearly 90; its hight is 

 about one-sixth its length; its foramen [delthyrium] is triangular and reaches the 

 beak, the width across the base being somewhat less than the hight; plications of 

 the surface are strong, direct and simple, but double their number on the umbo by 

 implantations, and agnin in the same way before reaching the margin, where they 

 number from thirty-six to forty-eight. Between the plicas are fine cross ridges 

 which sometimes rise to the tops of the plicae, but do not cross them so as to be 

 preserved in our specimens. A cast of the interior of this valve shows a distinct 

 general muscular impression, reaching a little more than one-third the perpendicular 

 diameter of the valve from the beak, and divided longitudinally into shallow furrows 

 and ridges converging within the beak, four of the former and five of the latter, with a 

 cross-striation visible on that portion between the teeth and near the foramen. The 

 central ridge in the general muscular impression on the cast does not reach the front 

 margin of the scar, but gradually dies out, giving place to the adjoining parallel fur- 

 rows which widen and coalesce, and show a longitudinal finer furrowing or striation. 

 The next ridges, on either side, are marked and prominent, extending to the anterior 

 angles of the scar, giving it a nearly straight, elevated front and angular corners, 

 somewhat as in 0. subquadrata. The two outermost ridges are fainter, but extend to 

 the lateral margins of the scar. Still, outside of all these ridges are traces of a 

 similar furrowing within the beak, embracing that portion between the teeth which 



