48 OBSERVATIONS ON THE ANIMALS 
north of France; three more in the green-sands of the English cre- 
taceous group, and at least three in the chalk ; but they do not seem 
to be ever very plentiful, and, owing partly, perhaps, to the ex- 
tremely thin shell, and partly to their shape, which is more exposed 
to injury than the flat shell of the Ammonite, they are scarcely ever 
obtained perfect. The shell is strengthened with ribs and tubercles ; 
the chambers seem to be numerous, and the last is very much 
larger than the rest. The siphuncle is, of course, dorsal, and is 
usually small compared with the area of the last septum. 
The Scaphite is found in the formations from the lias to the chalk, 
both inclusive. But one species (according to Fitton) is known in 
England below the chalk, although there is one in the French infe- 
rior oolite, and another in the lias at Wurtemberg. There are two 
more species known, both met with in the English chalk. There 
seems to be considerable difficulty in determining the real nature and 
use of the curious last chamber of the Scaphite. The inner part— 
that is, all the shell first formed by the animal—closely resembles an 
Ammonite, except that there is a slight puckering-up, as it were, 
of the shell, which indicates the genus; but how the last and outer 
chamber, which is larger than all the rest together, could, by any 
contrivance, be transformed into an inner coil as the animal grew and 
required a larger habitation, is a problem hardly yet attempted to be 
solved. Besides, in a state which we may suppose adult, the last 
chamber is sometimes turned round again in an opposite direction, 
and actually meets, and is partly closed up by, the inner whorls. 
We shall have more to say concerning this curious genus when we 
come to consider the probable nature of the animal. 
We have now arrived at the third genus named, the well-known 
and widely-extended Ammonites, a group of shells sufficiently mark- 
ed by more than one important character, and found throughout the 
long series of fossiliferous formations, from the very earliest to the 
chalk ; not scantily distributed, as the former genera, but most astonish- 
. ingly abundant, and including nearly three hundred species, varying in 
diameter from a line to more than four feet. The general shape of 
these shells is well known, and they have long attracted the atten- 
tion even of the least observant, under the name of petrified serpents 
which, by some unaccountable fatality, had all lost their heads. They 
may be seen in the cottage of the poor and in the drawing-room of 
the rich ; they may be picked up in the quarry or dug in the field ; 
and of all the innumerable proofs that surround us of the former 
existence of animals now extinct, none is more remarkable than the 
