8 
PROCEEDINGS OF THE ACADEMY OF 
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The external characters of this shell resemble those of Spir if era simplex, Phil. 
(Pal. Foss. p. 71, pi. xxix. fig. 124, and pi. lx. fig. 124), but the hinge-line is 
more elongate. 
This species, so far as is certainly known, is restricted to the base of the 
Burlington limestone. 
Syringothyris Halli, n. sp.—Shell of medium size, transversely elongate, 
widest along the hinge-line; greatest depth of the two valves equalling or ex¬ 
ceeding the greatest length. Ventral valve with a deep, defined sinus; beak 
very elevated ; surface sloping thence with but little convexity, to all parts of 
the margin,—being sometimes even concave between the apex and the cardinal 
extremities ; area large, triangular, transversely striate, flat or slightly arched, 
with a more marked incurvation just beneath the beak; perforated by a narrow, 
or moderately wide, triangular fissure, which is grooved along its lateral bor¬ 
ders as if for the reception of a deltidium; dental plates rather short—in a va¬ 
riety, very short—diverging at an angle of 66° ; mesial septum a low ridge ex¬ 
tending two-fifths the length of the valve ; line of divaricator scars extending 
with a curve from inner end of dental plates to inner end of mesial septum. 
Dorsal valve moderately ventricose, with a convex surface, and abrupt well- 
defined mesial elevation, and a small beak which overhangs the base of the 
fissure in the area of the opposite valve,—the area being scarcely perceptible 
in the dorsal valve. Surface ornamented by 12 to 16 rounded ribs on each 
side of the mesial fold and sinus, becoming obsolete toward the lateral angles. 
Mesial fold and sinus destitute of ribs. The whole surface is further marked 
by faint, delicate lines of growth. 
Length of hinge-line 1-32 (100) ; depth from beak of ventral valve to most 
prominent point of dorsal—which is nearly at right angles to the plane of the 
valves—-70 (53); distance from hinge-line to middle of anterior margin 
•54 (41) ; elevation of (ventral) area *48 (36) ; width of fissure at base 
•28 (21). 
Ranges through the yellow sandstones. In bed No. 1 is a variety with some¬ 
what convex area, very narrow fissure and very short dental plates. The species 
occurs also at Clarksville, Mo.,where the beak of the ventral valve is bent 
somewhat to the left (this beak being uppermost) in the style of a Streptorhyn - 
chus, producing a curvature of the mesial sinus and the fissure; and is further 
peculiarly marked by several distinct lamellar wrinkles of growth. 
Named in honor of Prof. James Rail, the eminent Paleontologist of Albany, 
N. Y. 
AVICULA, (Klein,) Bruguiere. 
Avicula Whitei, n. sp.—Shell large, transverse, exceedingly oblique, with 
nearly terminal beaks. Hinge-line more than three times the greatest dorso- 
ventral dimension. Anterior ear pouched, not distinctly divided from the body 
of the shell. Left valve ventricose ; umbonal ridge somewhat arcuate, or 
nearly straight, forming an angle of about 20° ? with the hinge-line ; slope 
thence to the ventral margin very rapid—to the dorsal side rather gradual and 
symmetrical to the very hinge-line—the posterior wing not being divided from 
the body of the shell. Ventral margin, in the middle rather straight and near¬ 
ly parallel with the dorsal; posterior margin sigmoidal by a deep, or rather 
shallow sinus, isolating the posterior end of the cartilage plate from the body 
of the shell; posterior wing triangular, exceeding the shell. External surface 
marked by numerous fine, irregular striae of growth. Right valve much. less 
ventricose, marked on the body and anterior slope by numerous sharp, regular 
raised concentric striae which become very faint posteriorly. Cardinal line in 
each valve with a long, slender, bifid lateral tooth behind the beak. 
Length of dorsal side 2-13 (100) ; greatest dorso-ventral dimension *70 (33) ; 
depth of left valve >"22 (10). 
Avicula acanthqptera, Hall, (Geol. Rep. 4th Dist. N. Y., p. 26jf).—Shell 
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