PLATE 29. 
Fig. 1. 490. 4. OrMOCERAS VERTEBRATUM. ( Pag. 94.) 
1 a. A fragment of the cast of a specimen, having the edges of the septa slightly projecting. 
1 b. Longitudinal section, showing the arching of the septa and form of the sipliuncle. 
1 c. A fragment where the laminae 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 siphuncle is hollow in tins 
specimen. 
1 d. A fragment of the siphuncle, and several of the septa attached. The siphuncle is worn down in part, 
exhibiting a section having the laminae thickened, while other portions retain their entire character. 
1 c. 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 the outer 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 rugae impressed upon 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 b. 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? 
Fig. 4 a, b. 
493. 
30. 
Orthoceras aeruptum. 
(Pag. 96.) 
(Pag. 97.) 
