Geology and Paleontology. 1103 
ceed. Acad. Nat. Sci., Phila., XII, 309. Spirifera strigosa Meek 
(1 860), to extra copies of the above cited paper. Spirifera.orestes 
Hall and Whitfield (1873), 23d Rept. Board of Regents on N. Y. 
State cabinet, P. 237, Spirifera strigosa Meek (1876), in Col. 
Simpson’s Report Expl. across the Great Basin of Utah, 347, pl. I, 
figs. 5,a,b,c,d. Compare with description of Spirifera orestes, of H. and 
W., 23d Report of Board of Regents on New York State cabinet of 
Nat. His., p.237; and also with description of Spirifera strigosua 
Meek, U. S. Geol. Exploration of Fortieth Parallel, Vol. IV., p. 43. 
Shell very variable; semielliptical, subouate, suborbicular, longer 
than wide or wider again than long; of medium or under medium 
size; often gibbous in young as well as old specimens; frequently 
greatly extended on the hinge line, sometimes hinge-line one-third 
less than the greatest width of the valves below; at other times the 
hinge-line and valves below are equal, valves subequal ; greatest 
convexity of the ventral valve at or slightly above the middle; 
greatest convexity of the dorsal valve at the centre, or a little above. 
eak of ventral valve strong and usually high, sometimes low; 
from slightly to very sharply incurved ; the height, strength and 
curvature of the beak varies somewhat with the age of the animal; 
central area high, concave, vertically striated ; foramen rather large, 
triangular, extending to the apex of the valve, the margins or 
dental lamellae strongly projecting in well-preserved specimens. — 
Valves marked by very large or small, simple, rounded or angu- 
lar plications; varying in number from four to thirteen on each 
side of the mesial fold and sinus, in young as well as adult forms. 
Mesial fold and sinus marked by from one to six bifurcating pli- 
cations (in some instances, the plications do not bifurcate, but run 
out along the margins of the fold and sinus). Usually the mesial 
fold is strongly elevated in front and more or less well defined to 
the beak, but in rare instances, even in adult specimens, the fold is 
not defined, even in front, although the sinus of the opposite valve 
is well defined to the beak, and produced in front. 
Mesial sinus more or less well defined to the beak, rather rapidly 
expanding below, and produced in front into a sharp or broadly 
rounded extension; bottom shallow or deep, angular or rounded. 
Surface of specimens, with small or medium-sized plications, marked 
y very fine strie parallel to the plications; surface of specimens 
with large, eoarse = oraa marked by stronger and more numer- 
ous obliquestriz, which unite with each other on thesummit of the pli- 
cations and centre of the depressions between the plications, thus 
giving the entire surface a very sharply zigzag striation ; the surface 
of many specimens are also crossed, in front, by slight lines of 
growth, 
Surface of the interior of the valves smooth or marked by ridges, 
which correspond to the depressions between the plications on the 
