FISHES OF THE CARBONIFEROUS SYSTEM. ihafa| 
marked, but in other, respects similar, plates in the Chemung. Of these 
species I append the diagnostic characters. 
BorTHRIOLEPIS LEIDYI, n. sp. 
Plate XVIII, Fig. 2; Plate XX, Figs. 1-5. 
Form and dimensions of the body unknown; surface covered with a 
number of angular, closely approximated, enameled plates, which are ellip- 
tical, subtriangular, or oblong in outline, and from one and a half to three 
inches in length by one to two inches wide ; the exterior surface is wholly 
occupied by a series of vermicular furrows or lines of hopper-shaped con- 
necting pits, which are often pierced or punctate at the bottom; this surface 
is also ornamented by three incised lines, which diverge from the center to 
the middle respectively of the posterior and the postero-lateral margins ; the 
inside of most of these plates carries a prominent keel along its central line 
for two-thirds of its length. 
Besides these, the more common form of plates, there are others which 
are much more highly arched and doubtless covered the lateral surfaces of 
the body. The head, but imperfectly shown in our specimen, was appar- 
ently much like that of Pterichthys, viz, was rounded in outline, strongly 
arched, and was covered with a series of polyg gonal plates with a dumb- bell 
aperture in the center. The pectoral organ was also similar to that of 
Pterichthys in form and markings; it was from four to six inches in length, 
terminating above in a hemispherical smooth head, composed of dense bony 
tissue, exhibiting a peculiar laminated structure. The proximal element is 
from one-half to three-quarters of an inch wide, gently curved and rounded 
or blunt-pointed at the extremity; the surface was formed by a series of 
angular plates, carrying the same ornamentation as the body plates. The 
distal portion was a slender spine articulating with or anchylosed to the 
upper portion, and was doubtless used as an organ of defense. At its base 
the surface was formed by a number of small plates ; toward the summit it 
is longitudinally striated. The point is sharp, and the outer margin is set 
with a row of relatively strong, acute, recurved denticles. This spine has 
been described by Dr. Leidy under the name of Stenac canthus nitidus.’ 
‘Jour. “Acad, Nat. Sci., , Phila., 2d series, vol. 3, p. 164, pl. 16, fig. 8. 
