BRACHIOPODA. 437 
Orthis (Plectorthis) whitfieldi.] 
Orvuis (PLecTORTHIS) wHITFIELDI N. H. Winchell. 
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, pl. xu, fig. 8. 
1892. Plectorthis whitfieldi HALL. Paleontology of New York, vol. viii, pt. i, p. 221, pl. v, fig. 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 bight 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 again in the same way before reaching the margin, where they 
number from thirty-six to forty-eight. Between the plice are fine cross ridges 
which sometimes rise to the tops of the plice, 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, witha 
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 O. 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 
