INTRODUCTION. 
Vll 
to bear upon the class he has with so much boldness and originality 
attempted to reclassify, the extremely revolutionary nature of the 
changes he has proposed in the minor divisions of his system (in- 
volving the wide separation of many forms hitherto associated to- 
gether) challenges the enquiry as to whether our knowledge of the 
developmental history of the Cephalopoda is not as yet far too imper- 
fect to justify such a radical departure from existing systems. The 
suppression of the familiar names Cyrtoceras and Gyroceras seems 
quite unnecessary, and seeing that the names Orthoceras and Nau- 
tilus are retained, in a restricted sense, in Hyatt’s scheme, there 
seems to be no good reason why the two former should not have 
been similarly used h The reasons are assigned in another part of 
this Catalogue for the adoption of Hyatt’s arrangement of the Gom- 
phoceratidse (infrd, p. 214), and also some of his divisions of the 
Cyrtocerata as subgenera of Cyrtoceras {infrd^ p. 262). In the 
remarks upon the genus Gonioceras occasion is taken to observe that, 
considering the imperfect condition of the specimens upon which 
that genus has been founded, it Avould be premature to form any 
conclusions as to its affinities, as Professor Hyatt has done. And, 
again, the genus Eudoceras, Hyatt C which is regarded by its author 
as related to Gonioceras, is very imperfectly known. Mr. C. E. 
Beecher ^ makes the following observations upon TrocJioceras? 
{Gonioceras ?) pandium^' Hall, the type of the genus Eudoceras : — 
“ Xo additional specimens of this species have been obtained since 
the original publication in 1879, and its generic relations are stiU 
uncertain.” 
Some authors, basing their classification upon the difference in the 
structure of the initial chamber in the Ammonoidea and the Xauti- 
loidea, have placed the former in the Dibranchiata, on the ground 
that the nucleus (protoconch) in the Ammonites agrees with that 
of Spirula rather than with that of the Xautiloids ■* *. Hyatt, 
^ See an able paper by Prof. Hyatt read before the American Association 
for the Advancement of Science, Minneapolis Meeting, Aug. 1883, entitled 
* Fossil Cephalopoda in the Museum of Comparative Zoology ’ (Cambridge, 
Mass.); also the memoir previously quoted. 
^ Proc. Boston Soc. Nat. Hist. vol. xxii. 1883, p. 287. 
’ Pal. New York, vol. v. pt. ii. Suppl. 1888 (contained in vol. vh. of that 
work), p. 37. 
Munier-Chalmas, Comptes Eendus hebdom. de I’Acad. des Sci., Dec. 1873; 
Douville (Bull. Soc. Geol. de France, 3^^ ser. vol. viii. p. 239, 1880) comes to 
the same conclusion as Munier-Chalmas, but upon different grounds, viz. : 
the form of the aperture in Ammonites {Morphoceras) pseudo-anceps, which 
