SUPPLEMENT. 
323 
Hyatt makes a special reference to it in his “ Genera of Fossil 
Cephalopods ” and he there places it in a separate family (Gonio- 
ceratidse), stating that Professor Hall considers his genus Eudoceras ^ 
as very closely allied to it. The genus Eudoceras is described by 
Hyatt as including “ straight shells of the Silurian and Devonian, 
with whorls flattened, sides angular,” &c. He also deflnes Gonid- 
ceras as having “ a broad winged shell, which in form and structure, 
as indicated by the septa and striae of growth, closely resembles the 
internal shells of Sepia ” ; and he considers that “ the facts are 
sufficient to warrant our assuming this \_Gouioceras'] as probably one 
of the passage-forms from the compressed Orthoceratites to 
the true Sepioidea, and possibly a more or less remote ally of 
PalcpMeuthis Eunensis, Poem., of the Devonian” 
There is, however, no reason whatever to doubt that the shell of 
Gonioceras was external, like that of Ortlioceras and Actinoceras, to 
the latter of which genera Gonioceras is by no means remotely 
related. On the other hand, the shell in the Sepioids is internal, 
and functions not as a habitat for the animal, but as an internal 
support, which, after dwindling to a horny plate in Loligo, totally 
disappears in Octopus'^. This difference in the function of the 
shells points to a different line of descent in the two groups to 
which the forms in question belong. 
Referring to certain species described by Billings ® under the names 
of Orthoceras Xipliias and 0 . liastatum, Barrande says that they 
“ may be considered as establishing a sort of transition between the 
^ Proc. Boston Soc. Nat. Hist. vol. xxii. 1883, p. 288. 
^ Referring to the Supplement to vol. v. pt. ii. of the ‘ Palaeontology of New 
York,’ contained in vol. vii. of that work (.dated 1888), no such genus as Euclo- 
ceras is to be found, though I am informed by Mr. 0. E. Beecher, of Albany, 
N. Y., that the species adopted by Prof. Hyatt as the type of his (not Hall’s) 
genus is Trochoceras'i {Gonioceras'^) pandum. Hall. This species is fully 
described in vol. v. pt. ii. Palaeont. of N. Y. 1879, p. 403, pi. cxi. f. 4. The 
strongly inflated upper part of the shell (specially observable in Hall’s fig. in 
the SujDpl. to vol. V. pt. ii. Pal. of N. Y. pi. cxvii. f. 3) gives this species very 
much the aspect of a Gomphoceras ; it is too imperfect to warrant the applica- 
tion of a new generic name. 
^ This fossil, however, has been pronounced to be the dermal plate of a placo- 
ganoid fish (see Zittel’s Handb. der Palaontologie, Band i. Abth. ii. footnote, 
p. 521. This species was described at first under the genus Archceoteuthis (1854) 
by Roemer, and subsequently referred by him to d’Orbigny’s genus PalcBoteuthis 
(Palseontographica, Band iv. 1856, pp. 72-74). 
^ Except that the rudiments of the shell-sac appear in the embryo, and then 
evanesce. (Lankester, Encycl. Brit, 9th ed. vol. xvi. Mollusca, p. 672.) 
® Geol. Surv. of Canada, Rep. of Progress, 1853-1856, pp. 318, 333 (1857). 
T 2 
