PLATE XCIX. 
Gyroceras spinosum. 
Page 382. 
See Plates 47, 48, 49, 98. 
Fig. 1. Lateral view of a compressed specimen, preserving the chamber of habitation and about thirty air- 
chambers, showing the curvature of the tube and the increase in the deplh of the air-chambers 
from the apex to the grand chamber. The internal mould shows the bases of two lateral rows 
of semi-tubular spines. 
Fig. 2 id. A gutta-percha impression of the matrix, showing the characters of the surface ornamentation 
more clearly than is preserved on the internal cast. Toward the aperture the tube is orna¬ 
mented by transverse expansions of the test, with the bases of the spines preserved as sinu¬ 
osities of the margins. 
Fig. 3. Ventral view of two air-chambers, showing portions of the siphuncle exposed in the process of 
weathering. 
Fig. 4. A small chambered fragment, showing the siphuncle as in the preceding. 
Fig. 5 id. A septum showing the position of the siphuncle and the transverse section of the tube, which has 
been disturbed by compression. 
Fig. 6. The chamber of habitation of a small individual associated with this species, showing its proportions 
and the concavity of the last septum. 
Fig. 7 id. The septum, showing the position of the siphuncle and the transverse section of the tube, slightly 
disturbed by compression. 
Fig. 8. The septum, at the base of a large chamber of habitation, showing the transverse section of the tube. 
This specimen and the preceding are referred with some doubt to this species, as they do 
not possess distinctive characters. 
The specimens here figured are from the Schoharie grit, at Schoharie, N. Y. 
