XX 
TXTK0DT7CTI0X. 
Trias by means of the sculpture of their shells. He distinguishes 
two subfamilies — OyroceratincB and Nautilino ’ — under the famil\ 
Nautilidce; and in the Gyroceratinse he includes the Carboniferous 
genera Temnocheilus, M‘Coy, and Trematodiscus, Meek and AYorthen, 
and the Triassic genus Pleuronautilus, Mojs. These he regards as 
distinct genera, and supposes that the two former were in all 
probability derived from Gyroceras, at about the beginning of tho 
Carboniferous epoch. The subfamily Nautilincn is represented in 
the Alpine Trias by 26 species, of which, accordiug to Mojsisovics, 
19 belong to the genus Nautilus, and 7 to Clydonautilus. Hyatt ‘ 
has, however, placed two of the former, viz. N. Carolinum and 
N. Tintoretti, in his genus Cenoceras. Zittel^ assigns only sub- 
generic value to the various divisions of the genus Nautilus; while 
Pischer^, though he enumerates Meek’s subdivisions, apparently 
attaches no importance to them; and Blake ^ selects only one of 
them — Discites — as a subgenus of Nautilus. 
Table B is designed as a convenient reference to the strati- 
graphical divisions adopted in the text. It is based, with some 
modifications, upon the table furnished by Mr. J. E. Marr in his 
“ Classification of the Cambrian and Silurian Bocks ” (1883). 
The subdivisions of the British rocks are those employed by Mr. H. 
B. Woodward in his ‘Geology of England and Wales’ (2nd ed., 
1887). Dr. Schmidt’s paper “ On the Silurian (and Cambrian) 
Strata of the Baltic Provinces of Bussia, as compared with those of 
Scandinavia and the British Isles,” ® has also been consulted in 
compiling the table. 
Many attempts have been made, with more or less success, to 
correlate the minor divisions of the Xorth- American Palmozoic 
rocks with those of Europe. Professor Lapworth® has recently 
contributed towards this object by working out the graptolitic 
zones of the Lower Palaeozoic rocks of the river St. Lawrence at 
and below Quebec, and has shown the relations between those 
rocks and the rocks of the same age in Great Britain, Continental 
Europe, New York State, and Canada, by means of their graptolitic 
fauna. 
^ Proc. Boston Soc. Nat. Hist. toI. xxii. 1883, p. 300. 
^ ‘ Handb. der Palseontologie,’ 1884, p. 379. 
’ ‘ Manuel de Ooncbyhologie,’ fasc. iv. 1882, p. 414. 
*■ ‘ British Foss. Oeph.’ 1882, pt. i. p. 62. 
® Quart. Joui'n. Geol. Soc. 1882, vol. xxxviii. p. .514. 
* Trans. Roy. Soc. Canada, Sect. iy. 1886, p. 182 (Table A). 
