488 Transactions. — Geology. 



rounded and perforate. Alveolar cavity one-fourth the total length of the 

 guard. 



Var. y. — Lateral furrows long and deep, and curved to the dorsal aspect. 

 The length of the guard is five times that of the fifteen septa in the phrag- 

 maoone. The form of the guard is hastate, owing to the expansion of the 

 alveolar walls and the tapering of the apex. 



Var. §. — Guard sub-cylindrical, and constricted at the alveolus. Lateral 

 furrows short, and suddenly reflected to the dorsal aspect. Apex blunt, 

 with a terminal tubercle or knob. Length of alveolus one-fourth that of 

 guard. 



Var, e. — Lateral furrows short, deep, and bent towards the ventral 

 aspect. Guard de^Dressed on both dorsal and ventral surfaces. Apex sub- 

 conical. Angle of the phragmacone 25°. Septa very close, numbering 

 25-30. 



The series of sections exhibited illustrate the structure of this belemnite, 

 and especially display the mode in which the central portion of the guard 

 frequently exfoliates, casting from its interior a smooth fusiform body, 

 produced and slightly laminated in structure at the upper end, and blunt 

 with a minute depression or perforation at the lower end. These form the 

 Acanthoconiax of Miller, and have frequently been mistaken for spines of 

 Cedaris. They are not formed, as has been suggested, by the abrasion or 

 weathering of the guard of the belemnite, but are due to its structural 

 arrangement, which, notwithstanding the appearance of radiating prisms in 

 the interior, really consists of concentric laminae arranged in fusiform layers 

 round the central axis. In some of the specimens the axis is seen to be an 

 open canal filled with the sand of the imbedding matrix. This canal seems 

 to be continuous with the siphuncle that traverses the septa of the phrag- 

 macone, and to perforate or be a continuation of the conotheca, passing on 

 one side of the spherical pellet or nucleus that forms the apex of the 

 phragmacone. 



None of the varieties into which I have sub-divided Belemnites australis 

 can be considered to have a peculiar horizon or stratigraphical distribution. 

 The lower greeusand in the Amuri section has been divided as follows in 

 descending order : — 



1. Black grit or car-stone. 



2. Ajyorrhais ornata beds. 



3. Trigonia sulcata beds. 



4. Belemnite beds. 



5. Calcareous conglomerate, 



6. Wood sands. 



