BELEMNITES OF THE KIMMERIDGE CLAY. 



127 



Following the canal till it closes, the laniina? are seen to lose their truncations, and to 

 acquire the complete curvature. 



After careful study of many specimens, no doubt remains in ray mind that the canal 

 has been produced by the removal of the apices or terminal parts of the interior lamina- 

 of the guard. This process began at the alveolar cavity ; it happened during life, and 

 was occasioned by decay and absorption of the apices in the earlier stages of life. 



That these special parts might be of somewhat different composition from the other 

 parts of the laminte is suggested by some other cases in which terminal porosity and an 

 axial canal have been noticed ; and it is quite in agreement with two other cii'curastances 

 to be observed in these fossils. First, it is to be remarked that the alveolar cavity in these 

 Belemnites often appears marked by the undulated anterior edges of the lamina) of the 

 guard, which terminate in this cavity (see figs. 88, 91, 92), and show white, thin, sparry 

 plates, in consequence of the removal of parts of the laminae. And again, some of 

 the specimens show a curious appearance of a second canal going from the alveolar 

 cavity (figs. 90 and 92) near its apex. This, being carefully studied, is found to be occa- 

 sioned by the removal of some of the laminae of the sheath for a certain space inwards 

 from the alveolar cavity, leaving a kind of slit where the removal has happened. 



In later life the deposited sheaths were, in general, not removed by decay or absorp- 

 tion (see figs. 87, 88). 



ON THE BELEMNITES OF THE KIMMERIDGE CLAY. 



After diligent search in this clay near Oxford, where it is about 1 OOfeet thick, and is pretty 

 well exposed in brickyards and in quarries of the Coralline Oolite, and after a careful search in 

 the escarpment of Portland, I find, speaking generally, a remarkable accordance between 

 its Belemnites and those of the Oxford Clay known as B. abbreviatus excentrictis, B. Owenii, 

 and B. hastatm. This analogy was, perhaps, to be expected, inasmuch as Ammonites of 

 the groups of A. vertebralis and A. Uplex occur in both clays. 



Taking first the specimens allied to B. abbreviatus excentricus,\t would,! think, be difficult 

 to assign characters of sufficient weight to claim a specific distinction, though in old speci- 

 mens the ventral surface is more flattened towards the apex, and in yoinig specimens the 

 whole of the guard is depressed behind the alveolar region. In this respect the young 

 forms closely resemble those of B. Souichei (D'Orbigny, 'Ter. Jur.,' pi. xxii, figs. 4 — 8), 

 which was found in beds referred to the Portland scries at Ilauvringhen (Pas de Calais), 

 and at the Tour de Croi, near Boulogne. These forms differ from those of the same age 

 from the Oxford Clay and Coralline Oolite. 



Next, we may consider the longer forms, like B. Oicenii, of the Oxford Clay. Of these 



