PLATE 29. 



Fig. 1. 490. 4. OliMOCERAS VERTEBRATUM. (Pag. 94.) 



1 o. A fragment of the cast of a .specimen, liaving tlie edges of the septa sliglitly piojueling. 



1 b. Longitudinal section, showing the arching of the septa and form of I he .sipliuncle. 



1 c. A fragment where the lamina! of the shell have become silicified and separated, so that the septa and 



.siphuncle appear to be composed of double laminse. Tlie interior of the siphuncle is Iiollow in th's* 



specimen . 

 1 d. A fragment of the siphuncle, and several of the septa attached. Tlie sipliuncle is worn dowii in part, 



exhibiting a section liaving the lamina; thickened, while other portions retain their entire character. 

 1 e. A fl-agmcnt of the siphuncle, with parts of the septa attached. At the lower jiart the .shell is rcnioved, 



showing a ca.st of the interior of the siphuncle, having the contractions and expansions corresponding 



to those of the outer covering. 

 1 _/". A fr.agment having the walls of the sipliuncle broken down, and the cast of the interior standing out 



very prominently. 



1 g. A portion of the cast of the siphuncle enlarged, showing the ruga; impressed ujion it by the interior ru- 



gose surface of the siphuncle. 



Fig. 2. 491. 28. Orthoceras virgulatum. ( Pag. 96.) 



2 a. A small fragment preserving the .shell. 2 4. A section of the last. 



2 c. A silicified fragment broken through the centre longitudinally, except the lower part. 



Fig. 3. 492. 29. Orthoceras annulatum.? ( Pag:. 96.) 



Fig. 4 a, b. 493. 30. Orthoceras abruptum. ( Pag. 97.) 



