PLATE LIIA. 



Gyroceras trivolve. 



ra^e 374. 



See Plate 52. 



Fig. 1. Ventral view of a nearly entire inflividnal. fi-oin which the teat has been exfoliated, and showing' the 



charactei-s of the internal mould. Upper Helderbertf. Sdwlmrle, 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 ehown in the specimens. 

 Fig. 4. A longitudinal section of a small fragment, consisting of the chamber of habitation with two attached 



air-charabera. 

 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 siph uncle. 

 Fig. 6. A longitndinal 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 laciniosum. 



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. 



