BRACHIOPODA. 429 



Orthls (Dlnorthis) snbquadrata.] 



1873. Orthis aubquadrata MEEK. Palaeontology of Ohio, vol. 1, p. 94, pi. ix, flg. 2. 



1875. Orthis tubquadrata MILLEU. Cincinnati Quarterly Journal of Science, vol. ii, p. 38. 



1880. Orthis subquadrata WHITE. Second Annual Report, Indiana Bureau of Statistic-sand Geology, 



p. 484, pi. i, flgs. 3-5. 



1881. Orthis subquadrata WHITE. Tenth Report, State Geologist of Indiana, p 1 16, pi. I, flgs. 3-5. 

 1887. Orthis subquadrata SHALER. Fossil Brachiopoda of the Ohio Valley, p. 22, pi. vn. 



1892. Orthis fPlcesiomys) subquadrata HALL. Palaeontology of New York, vol. viii, pt. i, pp. 194, 



197, 222, pi. VA, flgs. 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 Meek, 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 denned; bracbial process rather strong 

 and directed obliquely forward and laterally; internal surface, excepting the radi- 

 iitely 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 



