60 EXPLANATION OF PLATES 39. 40. 



A portion of the outer shell is preserved at c. and im- 

 pressions of the fluted interior of the shell, which has fallen 

 off, are visible at d. (Original.) 



Plate 39. V. I. p. 263. Note. 



This Plate presents a longitudinal view of the same 

 fossil, of which a side view is given in the last figure. 

 The same transverse plates that approximate so closely 

 beneath the sides of the shell, where it is flat and feeble, 

 (PI. 38.) are distant from each other along the dorsal por- 

 tion, which from its convex form is strong. 



The Siphuncle is preserved in its proper dorsal place at d. 



The elevations and depressions of the transverse plate 

 in front of this figure exemplify the theory of Von Buch, 

 respecting the use of the Lobes and Saddles formed by the 

 undulations of its outer margin. See V. I. p. 267, and 

 Note. (Original.) 



Plate 40. V. I. p. 272. Note. 



Fig. 1. Ammonites Henslowi (Goniatites,) from Transi- 

 tion limestone in the Isle of Man. 



The Lobes are simple, and without foliations ; 

 their form resembles that of the slipper-shaped lobe 

 of the Nautilus Ziczac, and Nautilus Sypho. See 

 PI. 43. 



The lobes D. L. 1. V. are 'pointed inwards, and 

 the intermediate Saddles S. d. S. L. S. V. are 

 rounded outwards ; according to the type of Ammo- 

 nites. (Original.) 



Fig. 2. Ammonites striatus (Goniatites,) from the Coal 

 Shale of Lough Allen in Connaught, having its 

 lobes and saddles disposed in the same directions 

 as in Fig. 3, the delicate longitudinal stria? and 



