BRACHIOPODA. 429 
Ortlils (Dinorthls) subquiidrata.] 
1873. Orlhis subquadrata Meek. Palaeontology of Ohio, vol. i, p. 94, pi. ix, fli,'. 2. 
1875. Urthis subquadrata MiLLEit. Cincinnati Quarterly Journal of Science, vol. ii, p. ;i8. 
1880. Orthis subquadrata White. Second Annual Report, Indiana Bureau of Statistics and Geology, 
p. 484, pi. I, figs. .3-5. 
1881. Orthis subquadrata White. Tenth Report, State Geologist of Indiana, p 116, pi. i, figs. .3 r>. 
1887. Orthis subquadrata HuALKii. Fossil Brachiopoda of the Ohio Valley, p. 22, pi. vii. 
1892. Orthis ( Plaisiomys) subquadrata Hall. Palaeontology of New York, vol. viii, pt. i, pp. 194. 
197, 222, pi. VA, figs. 17-19. 
Original description: " Subquadrate, the cardinal line forming one side, the sides 
and base being nearly straight, with the angles rounded; cardinal line less than the 
width of the shell, extremities curved; area small, partially common to both valves; 
dorsal [ventral] valve nearly flat or slightly depressed near the margin, elevated 
towards the beak, which is small and well defined; ventral [dorsal] valve regularly 
convex with a shallow sinus along the center, producing a slight elevation of the 
dorsal valve in front; surface marked by uniform subangular radii, which bifurcate 
near the beak and again towards the margin, those near the cardinal line curving 
upwards; radii crossed by fine, elevated, concentric lines, which are very distinct in 
the depressions between the rays." 
The following more detailed description is that of l^eek, drawn up from speci- 
mens from typical localities: 
" Shell attaining about a medium size, rather distinctly resupinate, somewhat 
wider than long, subquadrate in general outline; moderately convex; cardinal mar- 
gin shorter than the breadth of the valves and rounding abruptly at the extremities 
into the lateral margins, which round and converge forward; front a little sinuous 
or straightened at the middle. 
" Dorsal valve more convex than the other, its most prominent part being near 
the middle; mesial sinus small and rather shallow, sometimes continued nearly to 
the umbo, or in other instances scarcely more than reaching the middle; beak very 
short, or little distinct from the edge of the area, and more or less arched; area 
narrow, directed obliquely backward and downward. Interior with scars of the 
adductor muscles moderately distinct, the posterior pair being situaed close back 
under the brachial processes, one on each side of a well defined rounded ridge that 
becomes suddenly smaller between the anterior pair; cardinal process rhombic, 
subconical, moderately prominent and having its posterior side marked by deeply 
impressed, divaricating striae; sockets well defined; brachial process rather strong 
and directed obliquely forward and laterally; internal surface, excepting the radi- 
a.tely striated front and lateral margins, nearly smooth. 
"Ventral valve a little convex at the umbo and flat or slightly concave between 
the umbo and the front and lateral margins, but sometimes having a low, very obscure 
mesial elevation towards the front; beak small and very short or scarcely equalling 
that of the other valve, arched at the apex, but not strongly incurved; area about 
