PLATE LI. 
Cyrtoceras citttm. 
Page 372. 
Fig 1 . 1. Lateral view of a small fragment showing the curvature of the tube, and the regular numerous 
annulations of the internal mould corresponding to the transverse ridges of the test. 
Fig'. 2. Ventral view of the preceding, showing the characters of the sinus in the lamellae. 
Fig. 3, Longitudinal section of a fragment of another individual, showing the curvature and enlargement of 
the tube, but preserving no traces of the septa. 
The specimens of this species here illustrated are from the Upper Helderberg limestone, at 
Schoharie, N. Y. 
GrYROCERAS Nereus. 
Page 373. 
Fig. 4. Lateral view of an individual, showing the depth of the air-chambers and the curvature of the tube. 
Fig. 5. The opp'osite view of the preceding which preserves, on this side, portions of the test with its orna¬ 
ments. 
Fig. 6. A portion of the surface enlarged, showing the plicate ridges and the fine, undulating lines of growth. 
Upper Helderberg limestone. Auburn, N. Y. 
