THE CEPHALOPODA 335 



TRIBE 2. PROSIPHONATA. 



The siphuncular necks project in front of the septa. The septal 

 sutures present deeply indented lobes and saddles. 



FAMILY 1. ARCESTIDAE. Globular and smooth or nearly smooth 

 forms, with a reduced umbilicus ; the terminal chamber very deep, 

 occupying nearly a whole whorl of the spire ; an aptychus present. 

 Genera Popanoceras, Gemmellaro ; Permian. Cyclolobus, Waagen ; 

 Permian. Arcestes, Mojsisovics ; Trias. Lobites, Mojsisovics ; Trias. 

 FAMILY 2. TROPITIDAE. The shells globular, but differing from those of 

 the Arcestidae in having radiating and tuberculated costae. Genera 

 Thalassoceras, Gemmellaro ; Permian. Tropites, Mojsisovics ; Trias. 

 Sibirites, Mojsisovics ; Trias. FAMILY 3. CERATITIDAE. Shells coiled, 

 with a large umbilicus ; the terminal chamber short ; sutures with 

 simple saddles. Genera Trachyceras, Laube ; Upper Trias. Ceratites, 

 de Haan ; Trias. Dinarites, Mojsisovics ; Trias. Some genera with 

 helicoidal shells are related to these coiled forms, viz. Cochloceras, 

 Hauer ; Trias : also some straight forms, e.g. Rhabdoceras, Hauer ; Trias : 

 they have been placed in distinct families by some authors. FAMILY 4. 

 PINACOCERATIDAE. Shell compressed, smooth ; the terminal chamber 

 short ; the suture very complicated, convex. Genus Pinacoceras, 

 Mojsisovics ; Trias. FAMILY 5. PHYLLOCERATIDAE. Shells coiled, the 

 whorls overlapping one another ; the suture formed of numerous lobes 

 and saddles. Genera Phylloceras, Suess ; Jurassic. Rhacophyllites, 

 Zittel. FAMILY 6. LYTOCERATIDAE. Shell discoid, the whorls loosely 

 united or uncoiled ; the sutures deeply indented but with only three 

 saddles and lobes. Genera Lytoceras, Suess ; Jurassic and Cretaceous. 

 Macroscaphites, Meek ; uncoiled and recurved ; Cretaceous. Hamites, 

 Parkinson ; flexed three times ; Cretaceous. Ptychoceras, d'Orbigny ; 

 Cretaceous. Turrilites, Lamarck ; coiled in a sinistral helicoidal spire ; 

 Cretaceous. Baculites^ Lamarck ; the adult straight and elliptic in 

 section ; Cretaceous. FAMILY 7. AMMONITIDAE. Shell coiled, with 

 narrow whorls which do not embrace one n n 



another ; aperture simple ; a horny anapty- 

 chus present. Genera Ammonites, Lamarck :; 

 Jurassic. Arietites, Waagen ; Jurassic. Aego- 

 ceras, Waagen, Lias. FAMILY 8. HARPOCERA- 

 TIDAE. Shell discoid and flattened, with a 

 carinated border ; the aperture provided with 

 lateral projections ; a calcareous aptychus, 

 formed of two pieces. Genera Harpoceras, F IG> 394. 



Waagen ; Jurassic. Oppelia, Waagen ; Jurassic. Morphoceraspseudoanc<>ps,ri S M- 



Lissoceras, Bayle ; Jurassic and Cretaceous. side view - a -. orifice for arms ; 

 -P, ' . , ,, - e.o, eye-orifice ;s.b.o, infundilralo- 



TAMILY y. AMALTHEIDAE. bhell flattened, buccai orifice. (After Douviiie.) 

 with a prominent carina continued anteriorly 



into a rostrum. Genera Amaltheus, Montfort ; Lias. Cardioceras, 

 Neumayr ; Jurassic. Schloenbachia, Neumayr ; Cretaceous. FAMILY 10. 

 STEPHAXOCERATIDAE. Shell not carinated, but with radiating costae, 

 which are often bifurcated ; aperture often provided with lateral pro- 



