WHITE. | CARBONIFEROUS FOSSILS 133 
Genus RHYNCHONELLA Fischer. 
RHYNCHONELLA ENDLICHI Meek. 
Plate 33, figs. 4 a and b; and Plate 36, figs. 2 a4 and b. 
Rhynchonella endlicht Meek, 1875, Bull. U. S. Geol. Sur. Terr., 2d ser., No. 1, p. 47. 
Although Mr.. Meek, when he originally described this species, be- 
lieved it to have been derived from strata of Upper Devonian age, sub- 
sequently ascertained facts lead me to believe that those strata really 
belong to the lower portion of the Carboniferous series. I therefore in- 
clude it among the Carboniferous fossils of this article. The following 
is Mr. Meek’s description of the species, together with his remarks 
upon it: 
“Shell attaining a rather large size, subtrigonal, with breadth nearly 
or quite equaling the length, the widest part being in advance of the 
middle, becoming very convex anteriorly with age; posterior lateral 
margins straight or but slightly convex in outline, laterally compressed ° 
or flattened, and diverging from the beaks, in adult specimens, usually 
at about right angles or less; anterior lateral margins rounding to the 
front, which is generally more or less produced, and, as seen in direct 
view from above or below, transversly truncated, or a little sinuous at 
the middle, the elevation increasing rapidly to the front, which is raised 
so astoform a very prominent, broad, rounded, or somewhat flattened and 
slightly defined mesial fold, rarely traceable back to the central region, 
while on each side the lateral slopes descend abruptly to connect with 
those of the other valve; beak moderately prominent, and incurved more 
or less nearly at right angles to the general plane of the valves; interior 
with a prominent mesial septum extending forward nearly half way to 
the front. Ventral valve flattened at the umbo, and so broadly and pro- 
foundly sinuous from near the same, anteriorly, as to leave onlya prom- 
inent angular margin on each side, the sinus being broadly flattened 
along the middle, and increasing rapidly in depth to the front margin, 
which is curved upward more or less nearly at right angles to the plane 
ot the valves, and produced in the middle, in the form of a large exten- 
sion, fitting into a corresponding sinuosity in the middle of the front of 
the other valve; anterior lateral margins on each side of the sinus meet- 
ing those of the other valve at acute angles; posterior lateral margins 
very abruptly deflected, and rectangularly deflected along each side of 
_ the sinus, to meet those of the other valve; beak comparatively small. 
“Surface of both valves ornamented by numerous radiating coste, 
which, on the umbones, are merely distinct raised lines, but increase 
in size anteriorly, particularly those in the sinus and on the mesial fold, 
where, toward the front of adult specimens, they become moderate sized, 
rounded ribs, of which four or six to seven may be counted in the im- 
mediate flattened bottom of the sinus and two or three more on the fold, 
while those on the lateral slopes bifurcate and continue of smaller size 
to the anterior and antero-lateral margins. Finer surface markings un- 
known. 
“Length of an adult specimen, 1.78 inches ; breadth, 1.53 inches; con- 
vexity, about 1.24 inches. 
“This is a fine species, more nearly resembling some Devonian and 
Upper Silurian forms than the usual Carboniferous types. Its most 
marked features are the large size of its mesial sinus, formed by the 
