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PROCEEDINGS OF THE ACADEMY OP 
long as the greatest width of the shell, forming a rounded right angle 
with the short lateral margins ; area triangular, three and a half times as 
long as high, arched in the quadrant of a cylinder, striated in both directions, 
pierced by a foramen reaching to the very apex of the beak, nearly twice as 
high as broad, rounded at its upper angle. Mesial sinus deep, broad, regular, 
beginning at the apex of the beak, the bounding ribs forming with each other 
an angle of about 22° ; on each side of the sinus five large plications, of which 
only the first three reach the beak, the others terminating at the area ; these 
are crossed by sharp, neat, imbricating lamellae of growth, of which, in the 
middle of the valve, about four occur in one-tenth of an inch. Dental plates 
short, columnar ; a median internal septum reaching from a point a little 
posterior to the teeth, as far as the middle of the.valve, thick at the bottom, 
thinned to an edge above. Internal surface of valve marked with numerous 
indented punetations. Dorsal valve unknown. 
Length, *48 (71); breadth, *68 (100); length of hinge line, *52 (79); 
height of area, -15 (22) ; convexity of ventral valve, *22 (33). 
From the Lithographic limestone, Clarksville, Missouri. “ White Collec¬ 
tion ” of the University of Michigan. 
This species bears perhaps too close a resemblance to S. solidirostris, White. 
The single valve, however, on which the species is founded, is more convex, 
with more rounded ribs, less regular lamellae, a higher area and more incur¬ 
ved beak. This is the specimen referred to by White, (Boston Proc. ix. 25,) 
and doubtfully identified with S. subtexta , White—a Burlington limestone 
species. 
Spirifertna binacuta, n. sp. Shell of moderate size, transverse, with nu¬ 
merous rounded ribs and attenuate hinge extremities. Dorsal valve some¬ 
what ventricose in the middle, regularly arched from anterior margin to the 
beak, becoming depressed toward the lateral extremities. Hinge line elon¬ 
gate, thickened at the margin, abruptly acuminate. Area narrow and long. 
Mesial fold little elevated above the general surface, divided by a furrow into 
two ribs, which, in old specimens, are again divided ; ten or eleven rounded 
ribs on each side of the mesial fold, of which the last two or three are subob- 
solete. External surface finely and regularly lamellose. Substance of shell 
thin and apparently possessing a rather coarsely punctate structure. 
Length of hinge line, *78 ; length from beak to base, -30. 
This species is readily distinguished by its auricular acuminations and pli¬ 
cate mesial fold. 
From the base of the Burlington limestone. “White Collection” of the 
University of Michigan. 
Spiriferina solidirostris, White. From near Hamburg, Illinois. “White 
Collection.” The ribs are more rounded than in the specimens from the Bur¬ 
lington sandstone. The same species occurs associated with S. binacuta in 
the base of the Burlington limestone. 
RHYNCHONELLA, Fischer de Waldheim. 
Rhynchonella ? tetraptyx, n. sp. Shell minute, subcircular in outline, 
with few and deep plications. Ventral valve moderately convex, highest in the 
middle, with a straight projecting beak, which is circularly perforate at apex, 
with a triangular opening below to the hinge. Along the middle of this valve 
is a very deep and very narrow sinus reaching nearly to the beak, and bound¬ 
ed by a very prominent rib on each side, beyond which is another smaller rib, 
making four in all. Dorsal valve almost strictly circular, with the same con¬ 
vexity as the ventral, highest also in the middle, with the inconspicuous beak 
closely appressed, and the middle raised into a strong plication or rib corres¬ 
ponding to the sinus or furrow of the ventral valve ; on each side of this rib 
[July, 
