35 



= Rhabdites, De Haan, 1825. 

 = Omphalia, „ 

 = Globites, „ „ 

 =Aganides {pars), D'Orbigny, 1826. 

 =Aganites (pars), Quenstedt, 1834. 

 =Aturia (pars), Brown, 1835. 

 = Hamites (pars), Fischer, 1837. 

 = Trocholites (pars), Conrad, 1838. 

 = Simplegas (pars), Sowerby, 1842. 

 = Discites (pars), McCoy, 1844. 

 = Discus (pars), King, „ 

 = Cryptoceras (pars), D'Orbigny, 

 1850. 



= Trematodiscus (pars), Meek, 1861. 

 Rh yncholithes, Faure-Biguet, 1819. 

 = Conchorynchus, De Blainville, 

 1827. 



= Rhynchoteuthis, D ' Orbigny, 

 1847. 



22. Discoceras, Barrande, 1867 



23. Ophidiocbras, Barrande, 1867 



24. Gyroceras, De Koninck, 1844 



= Gyroceratites, H. von Meyer, 1829. 

 = Hortolus, Steininger, 1831. 

 = Spirilla, Goldfuss, 1832. 

 = Lituites, Quenstedt, 1834. 

 = Cyrtocera (pars), Minister, 1839. 

 = Cyrtoceras (pars), Phillips, 1841. 

 = Cyrthoceratites ( pars), D' Archiac, 

 1842. 



Comprising the beaks of the Nautilus 

 animal. 



Turns of the shell touching, siphuncle 

 variable ; aperture of exterior chamber 

 open, its edge not contracted ; Silurian. 



Turns of the shell touching ; siphuncle 

 variable ; aperture of exterior chamber 

 contracted; Silurian. 



Turns of the shell not in contact ; siph- 

 uncle marginal, on external (convex) 

 side ; last chamber somewhat small, 

 edge without fold ; from Silurian into 

 Carboniferous. 



2. Shell an arc of a Spiral, in the same plane. 



25. Cyrtoceras, Goldfuss, 1832 



= Orthoceratites, Lamarck, 1799. 

 = Orthocera (pars), Sowerby, 1812. 

 = Campulites, Deshayes, 1832. 

 = Lituites (pars), Quenstedt, 1836. 

 = Cyrtoceratites, D' Archiac, 1842. 

 = Trigonoceras, M'Coy, 1844. 

 = Campyloceras, ,, ,, 

 =Aploceras, D'Orbigny, 1850. 



26. Cyrtocerina, Billings, 1865 



27. Oncoceras, Hall, 1847 



28. Streptoceras, Billings, 1866 



29. Piloceras, Salter (read 1858), 1859 



Shell slightly curved, never forming a 

 complete revolution ; siphuncle variable 

 in position, generally on convex side; 

 exterior chamber open, its edge not 

 contracted; from Silurian into De- 

 vonian. 



Shell like Cyrtoceras, but shorter and 

 thicker; Silurian. 



Shell slightly curved, pear-shaped; si- 

 phuncle lateral, edge of exterior chamber 

 contracted in the middle ; Silurian. 



Shell slightly curved, pear-shaped, edge of 

 exterior chamber contracted to form 

 three lobes ; Silurian. 



Same as Cyrtoceras, but the septa forming 

 a series of conical partitions, pointing 

 towards the smaller (earliest) part of the 

 shell; Silurian. 



