PTEROPODA. 
197 
transversely, and somewhat curving longitudinally. Dorsal side strongly 
convex transversely, the two inclined faces meeting in a prominent, obtuse 
angularity along the middle of the length, slightly incurved or concave in 
a longitudinal direction. The aperture is oblique; the peristome on the 
dorsal side receding in a broad sinus, which has a depth of fully half the 
width of the shell at that point. Operculum unknown. The imperfect 
specimens give no evidence of the presence of septa. 
Surface unknown, the shell not having been preserved. The casts present 
faint evidence of transverse strige, which are also shown in a gutta-percha 
impression, from a mould of the external surface in figure 20. 
This species, in its full extent, has had a length of more than one hundred 
millimetres, and the width of the shorter fragment at base is about thirty-five 
millimetres. The larger fragment, if complete, would have a width of about 
fifty millimetres. 
Formation and locality. In the Schoharie grit at Schoharie, N. Y. 
Hyolithes aclis. 
PLATE XXXII, FIGS. 22-30 ; AND PLATE XXXII A, FIGS. 23, 24, 25. 
Hyolithes aclis, Hall. Illustrations of Devonian Fossils: Pteropoda, pi. 27, figs. 5, 6, 7, 10 and 11. 1876. 
Form an elongate triangular pyramid, gradually and regularly tapering to an 
acute extremity. Transverse section somewhat semi-elliptical or subtri- 
angular, a little convex on the ventral side, about twice as wide as 
high; the lateral margins obtusely angular, sometimes attenuate from 
compression. Ventral face gently convex, and slightly curving in a 
longitudinal direction; anterior portion extended in a subspatulate expan¬ 
sion. Dorsal face highly convex transversely, and obtusely angular along 
the middle; very slightly concave longitudinally. Aperture oblique, the 
margin extended on the ventral side; on the dorsal side the peristome is 
not fully determined, but is apparently nearly straight on the sides, with a 
sinus at the angle. Operculum in general form subelliptical, the body of 
