274 
OBSERVATIONS ON THE ANIMALS INHABITING 
MULTILOCULAR SHELLS, 
CHIEFLY WITH A VIEW TO THE GBOLOGICAL IMPORTANCE OF THE SUBJECT. 
By D. T. AnstEep, Esq. B.A. F.G.S. F.C.P.S. 
OF JESUS COLLEGE, CAMBRIDGE.* 
In a former paper on this subject, which ended rather abruptly, 
in consequence of a page of MS. having been mislaid, I was pro- 
ceeding, after certain general remarks, and some account of the 
family Nautilacea and two genera of Ammoneata, to describe the 
sub-genera of the important and widely-extended Ammonites ; and 
it may be remembered that the first of these, the Goniutztes, was the 
only one of which any extended account was given. Next in order, 
the Ceratites of de Haan were mentioned as occurring in the muschel- 
kalk beds of the continent ; and these differ chiefly from the Gonia- 
tites in the nature of the intersection of the chamber with the shell, 
which in the latter group is angular, whilst in the former it con- 
sists of a series of nearly regular curves, alternately semicircles and 
mere wavy lines. But there is a further difference, causing a nearer 
approximation to the true Ammonites, in this group ; for, instead of 
the shells being very round and smooth, as the Goniatites almost 
invariably are, they begin to be provided with tubercles, acting as 
a sort of compensation for a flattening of the spiral, which generally 
occurs when these are introduced : for this flattened form, not being 
so strong with the same thickness of shell as the more rounded shape 
and more perfect arch of the other group, the tubercles or bosses 
are introduced, “‘ superadding the strength of a dome to that of the 
simple arch at each point where these bosses are inserted.” 
Passing on now to the other Ammonites, we find the line of in- 
tersection already spoken of waved in a more and more complicated 
manner, till it resembles rather the edge of a parsley leaf, or the 
sutures of a skull, than any thing else one can compare it to, and at 
the same time the number of bosses or tubercles is increased, and 
additional contrivances for strength are introduced, the shel] often 
becoming extremely fragile and the siphuncle very minute. In the 
chalk Ammonites especially the shell is very thin ; and it is often a 
* Continued from page 50 of the last number. 
