THE CEPHALOPODA. 215 
2. Shell spiral, turns of the shell not in contact, in the same plane. 
60. Criooeras, d'Orbigny, 1840. =: Crioceratites, Leveille, 1837. = Tropseum, 
Sowerby, 1840. 
Cretaceous. 
3. Shell an arc of a spiral, in the same plane. 
61. ToxocERAS, d'Orbigny, 1840. 
From Oolitic into Cretaceous. 
4. Shell changing from a spiral, in the same plane. 
62. ScAPHiTES, Parkinson, 1811. 
Turns of the shell at first spiral, in contact, and overlapping, afterwards tangentially 
divergent ; finally recurved and not in contact ; Cretaceous. 
63. Ancylooeras, d'Orbigny, 1840. 
Turns of the shell at first spiral, not in contact, afterw^ards tangentially divergent ; 
finally recurved, and not in contact ; from Oolitic into Cretaceous formations. 
5. Shell forming straight and curved lines, in the same plane. 
64. Ptychoceras, d'Orbigny, 1840. — Ptychocerus, King, 1844. 
The shell at first straight, aftervs^ards curved, and next straight, the turns in contact ; 
Cretaceous. 
65. Hamites, Parkinson, 1811. = Baculita, Fleming, 1828. = Toxerites, 
Uafinesque, 1819. 
The shell at first straight, afterwards curved, and next twice repeating the process ; 
the arrangement forming a species of compressed spiral ; the turns not in contact ; 
Cretaceous. 
66. Hamulina, d'Orbigny, 1850. 
The shell at first straight, afterwards curved, next straight ; the turns not in contact ; 
Cretaceous. 
6. Shell forming a straight line. 
67. Baculites, Lamarck, 1801. = Llomaloceratites, Hiipsch, 1781. — Tiranites, 
Montfort, 1808. 
The shell slightly conical ; Cretaceous. 
