NATURAL SCIENCES OE PHILADELPHIA. 
117 
Missouri geologists to 0. Michelini (?). It is a small circular species, with 
extremely fine ribs or striae, apparently too obscure^for either 0. Michelini or 
0. Vanuxemi. 
Orthis flay a, n. sp. Shell small, transversely oval, slightly truncate on 
the cardinal side. Ventral valve convex, perceptibly flattened toward the 
anterior margin, though without a marked sinus ; most elevated near the 
slightly projecting beak ; area rather high and broad, triangular, with an 
equilaterally triangular foramen ; dental lamellae slender, short, diverging at 
an angle of about 80° ; occlusor scars small, together enclosing a longitudinally 
oval space, which reaches one-third the distance from the beak to the anterior 
margin ; a median internal ridge reaches from the beak to beyond the middle 
of the valve. The shelUwas evidently thin ; its surface marked by one hun¬ 
dred or more delicate radiating ribs, which increase by implantation. 
Transverse diameter of shell '50.(100); longitudinal diameter *39 (78); 
depth of ventral valve .12 (24). 
Burlington, Iowa, apparently from Bed “No. i.” at the base of the yellow 
sandstones. “ White Collection,” of the University of Michigan. 
This species is less circular than the forms referred to 0. Michelini , and has 
a more convex ventral valve and larger area. It differs from O. impressa, 
Hall, (Greol. Rep. 11th Dist. N. Y., p. 267, fig. 2), in its more transverse 
shape, smaller size, more convex ventral valve, and feebler sinus. 
Streptorhynchus lens? White, (Proc. Bos. Soc. Nat. Hist. ix. 28), “Wey¬ 
mouth, Medina County, Ohio, 80 feet below the conglomerate.” Whittlesey’s 
Collection. 
Streptorhynchus umbraculum ? Schloth. sp. From “coarse bedded sand¬ 
stone, next below conglomerate, Warren, Trumbull County, Ohio.” Whittle¬ 
sey’s Collection. 
A large, undetermined species from oolitic limestone, “No. 6,” Burlington, 
Iowa, probably belongs here. Collected by A. Winchell. 
Streptorhynchus inequalis, White sp. From Weymouth, Medina County, 
Ohio, 80 feet below conglomerate.” Whittlesey’s Collection. 
Streptorhynchus - sp. ? A single interior of a ventral valve from 
“near Ashland, Ashland County, Ohio,” resembles S. Chemungensis, var. 
pectinacea, Hall. (Pal. N. Y., Vol. iv.) It differs, however, in the possession 
of a longer hinge line, and distinct auriculations, and lacks the alternation in 
the size of the radial ridges. 
Pentamerus lentioularis, White and Whitfield. This species, described 
from the yellow sandstone of Burlington, occurs also in the base of the Bur¬ 
lington limestone. “ White Collection ” of the University of Michigan. 
SPIRIGERA, D’Orbigny. 
Spirigera Missouriensis, n. sp. Shell of moderate size, broadly ovate, mo¬ 
derately ventricose, with lamellose exterior. Ventral valve with an extended 
beak, turned up at right angles with the plane of the shell, and having a cir¬ 
cular perforation at its extremity. Between the beak and the dorsal valve is 
an external flattening simulating an area, but traversed by the incremental 
lines. Sinus a shallow but distinct groove, beginning at the beak, widening 
and deepening anterior to the middle, and near the middle becoming well 
characterized. Dorsal valve nearly circular, with straight hinge slopes, and 
obtuse beak closely incurved and concealed, though not in contact with the 
ventral beak. Mesial fold less distinct than the sinus of the ventral valve, 
arising near the middle of the valve. Both valves are marked by numerous 
strongly imbricating lamellse of growth. Greatest thickness through the 
middle of the ventral valve. 
1865 .] 
