264 
NATJTILOIDEA. 
RemarJrs. The genus Cyrtoceras (first called Cyrtocera) was ori- 
ginally established by Goldfuss for the reception of certain species 
of Cephalopods from the Devonian of the Eifel, published in von 
Dechen’s translation of De la Beebe’s ‘ Geological Manual.’ The 
new genus was briefly defined in the words “ Halbmondformig gebo- 
gene Orthocerae,” in a footnote to p. 536 of that work ; the following 
species being enumerated as belonging to it, viz. : — 
Cyrtocera semilunaris^ Goldfuss. 
dejyressa^ Goldfuss. 
compressa, Goldfuss {Orthocera flexuosa, Schloth.). 
ornata, Goldfuss. 
annulata^ Goldfuss. 
lineata, Goldfuss. 
Prom these semilunaris and annul ata may be at once eliminated, 
as they have neither been described nor figured. The species 
ornata has become Gyroceras ornatum. It was described and 
figured by d’Arch. and de Yeru. in the Trans. Geol. Soc. 1842, 
2nd ser. vol. vi. p. 349, under the name of Cyrtlioceratites ornatus, 
Goldf., Bonn Museum.” The species compressa must now he 
changed to Cyrtoceras {Ooceras') jiexuosum, Schloth. sp. This also 
was described and figured by d’Arch. and de Yern. at p. 351 of the 
work just mentioned, under the name of Phraymoceratites subven- 
tricosus, d’Arch. and de Yern., = Cyrtlioceratites compressus, Goldf., 
Bonn Museum.” Lastly, clepressa and lineata remain to bo disposed 
of, and as the former has been found in a more perfect condition 
than the latter, it may well be adopted as the type of the genus h 
Prof. Hyatt, in his Genera of Possil Cephalopods ”(Proc. Boston 
Soc. Nat. Hist. 1883, vol. xxii. p. 235), to which I have so often had 
occasion to refer, abolishes Cyrtoceras and Gyroceras from his system 
of classification, on the ground that they represent merely some of the 
stages through which Cephalopod shells pass in the course of race de- 
velopment. The following extracts may suffice to explain his views : — 
“ The young of nautilian shells p. e. shells that are close coiled as in 
Nautilus'] are identical with the adults of the arcuate [like Cyrtoceras] 
and gyroceran [L e. loose-coiled, like Gyroceras]^ and in different series 
repeat their forms, sutures, shell-markings, and the outlines of their 
whorl in transverse section. They are in succession, first arcuate, 
then gyroceran, and lastly nautilian or close coiled. 
“ In several series genetic lines of adult forms may be followed. 
^ Most of these particulars are taken from Barrande’s exhaustive history of 
the genus Cyrtoceras, contained in the Syst. Sil. de la Boheme, vol. il pt. i. 
pp. 375-475. 
