THE JURASSIC PERIOD. 237 
eating Sea-snails, such as the Limpets (Pave//ida), the Nerites 
(Nerita), the Turritelle, Chemnitzie, &c., still hold a predomi- 
nant place. The two most noticeable genera of this group 
are Cerithium and Verinea—the former of these attaining 
great importance in the Tertiary and Recent seas, whilst the 
latter (fig. 169) is highly characteristic of the Jurassic series, 
though not exclusively confined to 
it. One of the limestones of the 
Jura, believed to be of the age of 
the Coral-rag (Middle Oolite) of Bri- 
tain, abounds to such an extent in 
the turreted shells of /Verin@a as to 
have gained the name of ‘ Calcaire 
a Nérinées.” In addition to forms 
such as the preceding, we now for 
the first time meet, in any force, 
with the Carnivorous Univalves, in 
which the mouth of the shell is 
notched or produced into a canal, , 
giving rise to the technical name Fig. 169.—Nerinea Goodhallii, 
of “siphonostomatous,” applied to aed ham beirE gs Pa 
the shell. Some of the carnivorous ance presented by the shell when 
forms belong to extinct types, such Sale Audet re 
S ’ ngland. 
as the Purpuroidea of the Great Oo- 
lite; but others are referable to well-known existing genera. 
Thus we meet here with species of the familiar groups of the 
Whelks (Buccinum), the Spindle-shells (7uszs), the Spider- 
shells (Preroceras), Murex, Rostellaria, and others which are 
not at present known to occur in any earlier formation. 
Amongst the Wing-shells (£¢eropfoda), it is sufficient to mark 
the final appearance in the Lias of the ancient genus Cozz/aria. 
Lastly, the order of the Cephalopoda, in both its Tetrabran- 
chiate and Dibranchiate sections, undergoes a vast devel- 
opment in the Jurassic period. ‘The old and comparatively 
simple genus /Vawéi/us is still well represented, one species 
being very similar to the living Pearly Nautilus (2V. pompilius) ; 
but the Orthocerata and Goniatites of the Trias have finally 
disappeared ; and the great majority of the Tetrabranchiate 
forms are referable to the comprehensive genus Ammonites, 
with its many sub-genera and its hundreds of recorded species. 
The shell in Ammonites is in the form of a flat spiral, all the 
coils of which are in contact (figs. 170 and 171). The inner- 
most whorls of the shell are more or less concealed ; and the 
body-chamber is elongated and narrow, rather than expanded 
towards the mouth. ‘The tube or siphuncle which runs through 
