196 
Genus Tourritites, Lamarck.—Under this genus Professor 
Neumayer classes Helicoceras (fig. 46), with an open spiral, not 
in one plane, and Heteroceras, with a closed spiral only in the 
earlier stage of growth. In Turrilites (fig. 45), the suture-line 
Fie. 45.—Turrilites catenatus, d’Orb. Fic. 46.—Helicoceras Robertsoni, d’Orb. 
is divided into six lobes, each formed of a single pair of 
digitations. The ventral lobe formed of a pair which are a 
little longer or shorter than the lateral. The principal lateral 
and under lateral are formed of pairs of digitations and the 
columellar of single ones; the mouth is simple, and provided 
with bands on an anterior prominent process. 
ta a 
Genus Bacuuites, Lamarck.—This genus connects, according 
to Professor Nreumayr, Lytoceras with Hamuites in the structure 
of the principal lateral lobe. Baculites (fig. 47) has a straight 
conical shell. Mouth oval or compressed, provided on the 
Fia. 47.—Baculites anceps, Lamarck. 
ventral side with a projecting linguiform process and two 
lateral grooves, which extend to the opposite side of the shell. 
Septa symmetrical, divided into four or six lobes, each formed 
of a pair of digitations. The ventral lobe equals in length the 
