Xii INTKODTJCTION. 
Cenoeeras, Hyatt. Type, Nautilus] intermedins, J. Sowerby, Min. 
Concb. vol. ii. pi. cxxv. (1816). 
Cymatoceras, Hyatt. Type, Nautilus pseudoelegam, d’Orbigny, 
Paleont. rran9., Terr. Cr^t. vol. i. pi. viii. (1840). 
* Nautilus, Breyn. Type, Nautilus pompilius, Liune, Systema Naturse, 
10th ed. p. 708 (1758). 
Professor Hyatt’s system of classification (applicable alike to 
the IS’autiloidea and the Ammonoidea) is best explained in his 
own words ^ : — “It is a common mistake,” he says, “to designate 
my classification as ‘ embryological.’ It will be found by those who 
read these pages, that the whole life of the individual, and all its 
metamorphoses, have been deemed essential standards for the esti- 
mation of afiinities. Even the degradation al metamorphoses of old 
age are used as characteristics of value in the generic descriptions ; 
it is properly speaking an ontological classification.” 
It will be seen in the above Table that Professor Hyatt has added 
many new genera to those already established, and that he has 
distributed the whole in a series of Eamilies (all new, except Nauti- 
lidce), which, in conformity with his views, blends the straight with 
the curved forms 
It will also be observed that the family Nautilidee contains eight 
genera, including Nautilus. This genus, according to Hyatt, dates 
from the Jurassic period, the smooth forms of the Alpine Trias, such 
as Nautilus Carolinus, Mojs.^, N. Tintoretii., Mojs.'*, being referred 
by Hyatt to his genus Cenoeeras which has, however, for its type the 
well-known English Jurassic species, N. intermedins, J. Sowerby®. 
The following genera and subgenera of the Nautilidee are con- 
tained in the present volume : — 
Trocholites, Conrad, 1838. 43.) 
Gybocebas, de Koninck, 1844. {Infra, p. 53.) 
“ G-enesis of the Arieticlse ” (Smithsonian Contributions to Knowledge), 1889,. 
Preface, p. vii. 
^ See Part 1. of the present Catalogue, Introduction, pp. v-vii. 
® Die Cepbalopoden der Mediterranen Triasprorinz (Abhandl. d. k.-k. geol. 
Keichsanst. Band x.), 1882, p. 287. 
^ Ibid. p. 283. 
■’ Proceed. Boston Soc. Nat. Hist. 1883, vol. xxii. p. 300. 
® Infra, p. 192. 
It will be observed that this Table differs slightly from the one published 
in Part I. (p. xxiii), which it is intended to supersede. 
