PLATE LY. 
Gyroceras Matheri. 
Page 377. 
Fig. 1., Front view of the internal mould of an individual, showing the character of the annulations on the 
dorsal side of the outer volution, and the sinus of the ornaments on the ventral side of the apical 
portion. 
Fig. 2. Lateral view of the preceding, showing the volutions and the enlargement of the tube. The annula¬ 
tions and furrows of the crenulations are also shown. Upper Helderberg limestone, near Cats- 
kill, N. Y. 
Fig. 3. Ventral view of a larger individual, showing the sinus of the annulations on the internal mould, and 
the extension of the transverse lamellae into the surrounding matrix. Small fragments of the 
test are preserved on a portion of the tube, showing the surface-markings. Schoharie, N. Y. 
Fig. 4. Lateral view of the preceding, showing the curvature of the tube and the frequency of the annula¬ 
tions. This specimen exhibits a common tendency of the last half of the outer volution to 
become straight, and directed outward from the general curve of the spire. 
Fig. 5. A fragment showing more closely coiled volutions. The larger extremity shows the concave surface 
of a septum; but the longitudinal section, as represented, preserves no evidences of the air- 
' chambers or siphuncle. Schoharie, N. Y. 
Fig. 6. A septum showing the transverse section of the tube. 
