164 GEOLOGICAL SURVEY OF THE TERRITORIES. 
erushed and otherwise in a much damaged condition. The best exam- 
ple, which is represented by fig. 2 a on plate 40, shows that the original 
height of the body was about 45 millimeters, and its transverse diame- 
ter probably considerably less. 
The crushed condition of the specimens causes some doubt as to the 
true number of longitudinal rows of interambulacral pieces, but they 
evidently do not exceed five. There seems to be only four rows to each 
area, one row of comparatively large pieces, with two smaller rows upon 
the right-hand side of it, and one row on the left. This want of bilateral 
_ symmetry of the best preserved area in the example figured suggests the 
possibility that one row of smaller pieces on the left-hand side of the row 
of larger ones has been forced beneath the others by pressure, but a 
careful examination fails to demonstrate it. 
This species is clearly distinguished from ZL. coreyi M. & W., the only 
other known species of the genus, by the very much narrower interam- 
bulacral areas, the different and varying proportions of the pieces com- 
posing those areas, as well as some other important but less conspicu- 
ous differences. \ 
Position and locality.—Subearboniferous strata, probably equivalent 
with those of the Keokuk division, Salem, Washington County, Ind. 
MOLLUSCA. 
(MOLLUSUOIDEA.) 
BRACHIOPODA. 
(Genus ORTHIS Dalman.) 
ORTHIS THIEMEL White. 
Plate 41, figs. 4 a, b, ¢, and d. 
Orthis thiemei White, 1860, Jour. Bost. Soc. Nat. Hist., vol. vii, p. 231. 
Shell depressed, orbicular, usually a little wider than long, widest in 
front of the middle; binge line short. Dorsal valve deeper than the 
ventral valve, regularly convex, with the general exception of a very 
shallow median sinus which extends from front to about midlength of 
the shell where it becomes obsolete; beak projecting a little beyond the 
hinge line and slightly curving towards the beak of the opposite valve ; 
cardinal process strong, with a strong blunt-edged median septum ex- 
tending from it nearly half the length of the valve; brachial processes 
strong, slightly notched at the ends; margin crenulate in front. 
Ventral valve convex near the umbo, depressed in front, which, with the 
depression on the opposite valve, considerably flattens the front border; 
beak short, elevated and incurved, leaving but little space between the 
two beaks when both valves are in position; width and height of 
foramen about equal, nearly filled by the strong cardinal process of the 
dorsal valve; muscular cavity large, heart-shaped, with a more or less 
distinct forked septum occupying its middle. 
Surface marked with fine raised striew, which have occasional minute 
tubular openings upon them; the strize increasing in number by im- 
plantation, and traversed by the ordinary striz of growth and a few 
coarser imbricating lines. 
Length from 10 to 14 millimeters, 
