XVI 
INTR0DT7CT10N. 
stood that the numbers of species have been greatly augmented 
since Barrande’s lists were published, especially in the genera 
Orthoceras and Cyrtoceras ; but this would not materially affect the 
relative value of the figures just given. For the British and 
American species statistics have been prepared up to a compara- 
tively recent date. For the former Professor Blake, in his work 
on the British Fossil Cephalopoda \ records 62 species in the 
Ordovician. In the latter Miller^ shows that up to the year 1882, 
271 species of fossil Cephalopods had been described in the Ordo- 
vician rocks of North America. The Nautiloidea attained their 
greatest development in point of numbers of species in the Silurian. 
The Bohemian Basin alone has yielded to the labours of Barrande 
a total of 1062 species ; of these Orihoce^'cis counts 517 species, 
Cyrtoceras 328, Gomphoceras (including Phraymoceras) 124, and 
Trochoceras 49 ^ In North America about 151 species are 
enumerated in the Silurian, and in Great Britain and Ireland 204. 
All the old genera are represented in the Silurian, with the ex- 
ception of the following : — Endoceras^ Piloceras, Gonioceras, Dis- 
coceras^ and Conoceras', while the following have to be added, 
viz. : — Hercoceras, Adelplioceras, and Nothoceras ; but these are 
numerically unimportant, only one species each of Hercoceras and 
Nothoceras and two of Adelphoceras being known. The Devonian 
reached, a very considerable reduction takes place in the number of 
species, the total for all countries being given by Barrande'* (1877) 
at 242 species. When analysed these afford 131 species of 
Orthoceras^ 59 of Cyrtoceras^ 17 of Gyroceras, 14 of GomphoceraSj 
and 11 of Bactrites; the remainder being Nautilus 8, and Trocho- 
ceras 2 species. These figures would be somewhat below the mark 
at the present time, the N. -American species alone numbering, 
according to Mr. S. A. Miller, 167 species. The principal areas of 
Devonian species are North America, the Hartz, Westphalia, and 
the Ehenish Districts. The Carboniferous epoch saw the extinction 
of Trochoceras and Bactrites^ whose places were taken, so to speak, 
by a number of forms, hitherto assigned to the genus Nautilus, well 
* 1882, pt. i. p. 236, “ Table of Distribution.” 
^ ‘ Cat. of American Palaeozoic Fossils,’ 1877, and 2nd ed., Jan. 1883. 
^ Syst. Sil. de la Boheme, 1877, vol. ii. Suppl. et S^er. tardive, p. 266. 
See also G-eol. Mag. 1870, p. 486, in which an admirable summary is given of 
the contents of Barrande’s volunae on the ‘ Distribution of the Cephalopoda in 
Silurian Countries’ (1870). 
^ Syst. Sil. de la Boheme, vol. ii. Texte iv. Introduction, p. Ivi, 
