196 
PALEONTOLOGY OF NEW YORK 
along the centre, the angularity gradually disappearing toward the 
aperture. Aperture oblique, the shell on the ventral side extending 
forward in a broadly spatulate expansion, while the dorsal margin is 
broadly sinuate, the peristome being apparently slightly thickened. Oper¬ 
culum unknown. No traces of septa in any part of the body. 
Surface with some marks of arching transverse striae, which curve towards the 
aperture on the ventral side, and in the opposite direction upon the dorsal 
side, or parallel to the margins of the aperture. The ventral side presents 
two longitudinal depressed lines, which are faintly visible on the surface 
of the cast. These lines are nearly parallel to the lateral margins, and 
rather more than one-third of the distance from the margin to the center, 
but running to the margin a little distance below the apex. 
The typical specimen is represented in figs. 11, 12 and 13. The specimens 
figured are casts of the interior, the remains of the crystalline substance repre¬ 
senting the shell having a thickness of about one millimetre. 
A single specimen referred to this species is somewhat irregular in its mode 
of growth, and more attenuate towards the smaller extremity. In many 
respects this species is similar to what we may suppose to be the young of 
H. principalis; but that species is proportionally narrower in its upper part, and 
more abruptly expanding below. 
Formation and localities. In the Schoharie grit at Schoharie, and in the upper 
part of the limestone at Clarence Hollow, in Erie county, N. Y. 
Hyolithes principalis. 
PLATE XXXTI, FIGS. 17-21. 
Hyolithes principalis, Hall. Illustrations of Devonian Fossils: Pteropoda, pi. 27, figs. 17-20. 1876. 
Form an elongated triangular pyramid, which is slightly curving towards the 
dorsal side, apparently more abruptly expanding towards the aperture 
than in the upper part. A transverse section below the middle of the 
length is semi-elliptical, with a width twice and a half as great as the 
height; the lateral angles moderately acute. Ventral face gently convex 
