32 



fX. Clydonitidse 



Tetrabranchiata [continued) . 



(^XII. Ammonitidge', 



(53. 



Clydonites 



) 54. 



Choristoceras 



) 55. 



Rhabdoceras 



1 56. 



Cochloceras 



57. 



Ceratites 



\ 58. 



Baculina 



'59. 



Ammonites 



60. 



Crioceras 



61. 



Toxoceras 



62. 



Scapbites 



63. 



Ancyloceras 



64. 



Ptychoceras 



{ 65. 



Hamites 



66. 



Hamulina 



67. 



Baculites 



68. 



Turrilites 



69. 



Helicoceras 



70. 



Heteroceras 



L7L 



Anisoceras. 



ANALYSIS OF THE FAMILIES AND GENERA OF THE 

 FOSSIL CEPHALOPODA. 



First Order. — Dibranchiata, containing Section I. Octopoda, and 

 Section II. Decapoda. 



Section I. — (Octopoda) of First Order (Dibranchiata). 



I. — Shell involute, the turns in the same plane, thin, single chambered. 



Family, ArgonautidaB (Reeve, 1841). One fossil genus, Argonauta. 



I. Argonauta, Linne, 1758 Tertiary. 



Section II. — (Decapoda) of First Order (Dibranchiata). 



II. — Shell lance-shape, slender, with central ridge, generally termi- 



nating in a slight expansion of no great length without air 

 chambers. Family, Onychoteuthid.<e (Gray, 1847). Three fossil 

 genera, Enoploteuthis, Plesioteuthis, and Ommastrephes. 



2. Enoploteuthis, D'Orbigny, 1839... 



3. Plesioteuthis, "Wagner, 1860 



4. Ommastrephes, D'Orbigny, 1845 ... 



Sides sinuous, with lateral expansions ; 

 central ridge keeled ; Oolitic. 



Sides sinuous, with central and two side 

 ridges ; projection arrow-sbaped ; arms 

 with hooks ; Liassic. 



Sides generally straight, contracted to- 

 wards base, point expanded, central and 

 side ridges ; Oolitic. 



III. — Shell lance-shape, slender, with central keeled ridge, and side ex- 

 pansions of some length. Family, Gonatid^e. One fossil genus, 

 Loligo. 



5. Loligo, Lamarck, 1799 



Liassic. 



