PLATE LII A. 
Gyroceras trivolve. 
Page 37b 
See Plate 52. 
Fig. 1. Ventral view of a nearly entire individual, from which the test has been exfoliated, and showing the 
characters of the internal mould. Upper Helderberg. Schoharie, N- Y. 
Fig. 2. Front view of the preceding. 
Fig-. 3. Lateral view of the same, showing the number of volutions, the enlargement of the tube, and a 
more open spire than is usually shown in the specimens. 
Fig. 4. A longitudinal section of a small fragment, consisting of the chamber of habitation with two attached 
air-chambers. 
Fig. 5. A longitudinal section of a fragment, showing the concave surface of a septum at the larger extremity, 
but no traces of septa throughout the length. The material filling the tube was apparently 
deposited after the breaking or solution of the septa and siphuncle. 
Fig. 6. A longitudinal section of a portion of the outer volution of a specimen preserving the septa.' The 
specimen shows the siphuncular tube, continuing through the cavities of the air-chambers, and 
more septa than are here represented toward the aperture." 
Fig. 7. A transverse section, showing- the form of the tube toward the aperture. 
GYROCERAS LACINIOSEM. 
Page 376. 
Fig. 8. An end view of the matrix of a small fragment, showing' the regular plication of the transverse 
foliate expansions of the test. 
