EXPLANATION OF THE PLATES. 



jecting from them, and showing near the apex the accumulated nacrous matter, 

 which on decomposition formed the canal. 



Fig. 3. Illustrative views of fragments of Belemnites electrinus (see PI. VIII. figs. 18, 

 19, 20.) as found in Prussia, their cylindrical form arising from wearing down by 

 attrition before they M'ere imbedded in the sands in that country. 



Fig. 4. Pyritic cast of the chambered cone, showing the indentures formed by the 

 decomposition of the siphunculus, which cavities have been erroneously consi- 

 dered as spiraculae. 



Fig. 5. Transverse section of Belemnites fusiformis : p. 61. 



Fig. 6. Belemnites minimus : p. 62. 



Fig. 7. Illustrative views of the manner in which the laminae that form the guard of 

 Belemnites fusiformis are arranged : p. 61. 



Fig.S. Siliceous infiltrations in a portion of the guard of Belemnites ellipticus : p 60. 



Fig. 9. Casts in the conic cavity formed by the dropping out of the chambered shell ; 

 and in the grooves made by decomposition of a portion of the nacrous matter that 

 cements the two longitudinal halves together, as also in the central canal formed 

 by decomposition. — Casts of this description led to the theory that the supposed 

 central canal, extending from the siphunculus through the guard, divided into 

 two, which probably were nerves. 



Fig. 10. Belemnites minimus (see p. 55 & p. 62.) corroded, and converted into silex. 

 In the collection of Miss Benett, Norton-house, Wilts. 



Figs. 11, 12, 13. Appearance of decomposition, which has acted on the apex of a 

 Belemnite. This misled De Montford, when he formed his genera Cetocis and 

 Acamus. 



Fig. 14;. Sepia loligo : see p. 57, &c. 



Fig. 15. As MM. Cuvier and Lamarck agree with me in considering the inhabitant of 

 the Belemnite to have been a Sepia, I venture here to represent a Sepia resem- 

 bling loligo, but capable, on account of an abbreviated body, of insertion in the 

 outer chamber, whilst its muscles clasped the Belemnite, denoted by dots. 



Fig. 16. Spirula fragilis and its inhabitant : see p. 57. 



Fig. 17. Actinocamax verus : see Art. VI. p. 64. 



Fig. 18. Section of A. verus. 



PLATES X. XL XII. & XIII. 



Illustrate Mr. Lyell's paper on a recent Formation of Limestone in Forfarshire, &c. 

 Art. VIII. p. 73. 



Plate X. 

 Fig. 1. represents a section of the strata of part of Forfarshire, from the Grampians 

 on the north, to Dundee on the south, and shows the general structure of the 

 country between the Grampians and the Firth of Tay : see p. 73. 



This line of section (the course of which is expressed in the map, Plate XI.) 



v2 



