THE CEPHALOPODA. 
201 
and more or less straight in the interval. The bends few and never in contact. 
Septa transverse, divided regularly into six unequal lobes. Siphuncle marginal. Mouth 
round or oval, with or without processes or oval bands. All are Cretaceous forms, of 
which Hamites elegans^ d'Orbigny (fig. 92), is a good type from the Gault. 
k. /Species straight. 
Genus Baculites, Lamarck. Shell straight, conical, cylindrical or compressed, with 
parietes articulated by sinuous sutures. Septa approximate, perforate, and much fringed 
FiG. 93. — Baculites anceps, Lamarck. 
near the circumference. The last dwelling chamber is very large, and formed a long 
sheath. Siphuncle marginal. These straight Ammonites are found from the Neoco- 
mian formation to the Upper Cretaceous, Baculites anceps, Lamarck (fig. 93), is a 
type. 
/. Species with shell spiral and turreted. 
Genus Tuerilites, Lamarck. Shell spiral, turreted ; whorls contiguous, and 
exposed, with articulated walls formed by sinuous sutures (fig. 94). Spire dextral or 
sinistral, umbilicated throughout. Septa transverse, divided into six lobes, foliated at 
their margin. Mouth round. Siphuncle marginal, continuous. The Turrilites are true 
Cretaceous forms. Some species from the Lias were referred by d'Orbigny to this genus. 
These, however, have been proved to be only distorted species of Ammonites well known 
in the beds in which they are found. Type, Turrilites cate7iatus, d'Orb. (fig. 94). 
Fig. 9 4. — Turrilites catenatus, d'Orb. Fig. 95. — Eelicoceras Robertianum, d'Oib. Fig. 9G. — Iletoroceras Emerici, d'Orb. 
