THE, CRETACEOUS PERIOD: 273 
and Baculites. In the genus Crioceras (fig. 204, @), the shell 
consists of an open spiral, the volutions of which are not in 
Fig. 202.—Azcyloceras Matheronianus. Gault. 
contact, thus resembling a partially-unrolled Ammonite or the 
inner portion of an Axcyloceras. In Turrilites (fig. 203), the 
shell is precisely like that of the Ammonite in its structure ; 
but instead of forming a flat spiral, it is coiled into an ele- 
vated turreted shell, the whorls of which are in contact with 
one another. In the genus Scaphites (fig. 204, e), the shell 
resembles that of Amcyloceras in consisting of a series of volu- 
tions coiled into a flat spiral, the last being detached from the 
others, produced, and ultimately bent back in the form of a 
crosier ; but the whorls of the enrolled part of the shell are in 
contact, instead of being separate as in the latter. In the 
genus Hamites (fig. 204, f), the shell is an extremely elongated 
cone, which is bent upon itself more than once, in a hook-like 
manner, all the volutions being separate. The genus P¢ycho- 
ceras (fig. 204, a) 1s very like Hamites, except that the shell is 
only bent once; and the two portions thus bent are in contact 
with one another. Lastly, in the genus Laculites (fig. 204, 6 
and ¢) the shell is simply a straight elongated cone, not bent 
in any way, but possessing the folded septa which characterise 
the whole Ammonite family. The Aacudite is the simplest of 
all the forms of the Ammonzitide,; and all the other forms, how- 
ever complex, may be regarded as being simply produced by 
the bending or folding of such a conical septate shell in differ- 
ent ways. The Lacu/ite, therefore, corresponds, in the series 
of the Ammonitide, to the Orthoceras in the series of the Vau- 
tilide. All the above-mentioned genera are characteristically, 
or exclusively, Cretaceous, and they are accompanied by a 
number of other allied forms, which cannot be noticed here. 
Not a single one of these genera, further, has hitherto been 
detected in any strata higher than the Cretaceous. We may 
therefore consider that these wonderful, varied, and elaborate 
S 
