276 
PROCEEDINGS OP SOCIETIES; 
increasing the strength of the arch, and compensating for the lightness and 
delicacy of the materials that composed the frail habitation of this ancient Mol- 
lusca. This genus has been divided into fifteen sub-genera, including, in all, 
about three hundred species,—their size varying very much : some are not more 
than a line in diameter, whilst there are some found as large as a cart-wheel; the 
specimen on the table, from the lias of Badgworth, is upwards of two feet in 
diameter. Baculites are straight Ammonites, just as the Orthoceratites are 
straight Nautili: the six species of this genus- are altogether confined to the 
chalk. Harrates , so called from their hook-shape, are found in the upper oolitic 
and cretaceous systems: of the thirty species known, twenty-eight belong to the 
latter, and only two to the former. Scaphites are boat-shaped Ammonites, and 
their singular form is owing to the shell having taken a particular direction at a 
certain period of its development: they are found in the upper formations of the 
Secondary strata. Turrilites have a spiral shell, curled round like a winding 
tower, and gradually diminishing in diameter from the base towards the. apex. 
Of the seven species of this genus, one is found in the coral rag, three in the 
green sand, and three in the chalk ; thus the Ammonitidce may be traced through 
all the fossiliferous strata up to the close of the secondary period. The Ammo¬ 
nites extend through all the formations included between the transition limestone 
and the superior members of the cretaceous system : other genera, however, were 
introduced and terminated their career with particular systems or formations. 
The Orthoceratites are found only in the transition rocks, the Scaphites and Tur¬ 
rilites in the upper oolite and chalk, and the Baculites are confined to the latter 
formation : the Ammonitidce are entirely absent from the the tertiary strata. 
After describing numerous fossil genera of naked Cephalopodes, nearly allied to 
the Cuttle-fish, the lecturer proceeded to describe the internal organization of the 
Loligo, showing the relation of the horny internal rudimentary skeleton ; he next 
entered upon the history of those singular fossils which are so abundant in our 
locality, called Belemnites, and which once formed the internal skeleton of a naked 
mollusk, probably not unlike the Calmar (or Pen-and-ink-fish) of our coasts. 
He demonstrated the complicated structure of these singular fossils, and showed 
how they were composed of three distinct portions—-first of an elongated cone, 
which is more or less compressed, and, when fractured, is seen to be composed of 
a remarkable calcareo-fibrous structure, which, when burned, gives out a strong 
smell: the fishes radiate from the centre. Secondly, of an alveolus or chambered 
shell, embedded in the substance of the fibrous cone. Thirdly, of a delicate 
Sheath, which expands from the base of the elongated cone, and was destined to 
lodge and protect the ink-bag which has been found in situ in some specimens 
Obtained from the lias. The Belemnitidce were introduced into the seas that 
deposited the oolitic system: seventy-five species are found in the lias and oolites^ 
