66 EXPLANATION OF PLATE 44'. 



Fig. 16. Scaphites Equalis, from Chalk near Rouen, in 

 the collection of Mr. J. Sowerby ; the sides of the 

 external shell are strengthened and ornamented by 

 ribs and tubercles ; and the edges of the transverse 

 plates disposed in sinuous foliations (c.) as in Am- 

 monites. The mouth or outer margin (b.) returns so 

 nearly into contact with the air chambers (c), that 

 the want of space at this part for the expansion of 

 arms and head, makes it probable that the Scaphite 

 was placed entirely within the body of its animal. 

 (Original.) 



Fig. 16. Transverse section of the chambered portion of 

 Fig. 15, shewing the arrangement of the lobes and 

 saddles to be similar to that of Ammonites; the 

 siphuncle also is seen on the dorsal margin at a. 

 (Original.) 



Fig. 17. Longitudinal section of the calcareous Sheath 

 and Alveolus of a Belemnite. 



a. Alveolus, or internal shell, divided by transverse 



Septa into air chambers. See V. I. p. 373. 



b. Siphuncle, passing along the margin of the air cham- 



bers. 



c. Apex of the fibro-calcareous sheath, or solid Cone of 



the Belemnite. 



Plate 44'. V. I. p. 371, et seq. 



Illustrations of the probable nature of the Animals that 

 gave origin to Belemnites.''^ 



* In the descriptions of PL 44'. and PI. 44". the following letters 

 indicate the same parts in each specimen to which they are applied. 



a. The Apex of the calcareous shell, or sheath. 



b. Alveolar portion, or chambered shell. 



c. Ink-bag. 



d.i Portions of the thin anterior horny sheath, sometimes higlily 



e. } nacreous. 



/. Neck of Ink-bag. 



