PLATE 29. 



Fig. 1. 490. 4. OiiMocERAs vertebratum. (Pag. 94.) 



1 a. A fragment of the cast of a specimen, having the edges of the septa slightly projecting. 



1 6. Longitndinal section, showing the arching of the septa and form of the siplmucle. 



1 c. A fragment where the laniin<e of the shell have become silicified and separated, so that the septa and 



siphuncle appear to be composed of double laminae. The interior of the siphnncle is hollow in tlis 



speciraea. 

 1 d. A fragment of tlie^siphnncle, and several of the septa attached. The siphuncle is worn down in part. 



exhibiting a section having the laminas thickened, while other portions retain their entire character. 

 1 e. A fragment of the siphuncle, with parts of the septa attached. At the lower part the shell is removed, 



showing a cast of the interior of the siphuncle, having the contractions and expansions corresponding 



to those of tlie out«r covering. 

 1 /. A fragment having the walls of the siphuncle 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 rugas impressed upon it by the interior rv.- 



gose surface of the siphuncle. 



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



2 a. A small fragment preserving the shell. 2 6. A section of tlic last. 



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



Fig. 3. 492. 29. Orthgceras annulatum.? (Pag. 96.) 



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



