Till 
INTRODUCTION. 
however, has found the “ shrivelled remains of the protoconch” m 
two species of Orthoceras — 0. elegans^ Miiust., and 0. unguis^ Phill. , 
which he has figured in ‘ Science ’ (vol. iii. no. 22, Feb. 1, 1884, 
p. 126). But the importance of such a character for purposes of 
classification is very doubtful. As Dr. Zittel ^ has pointed out, no 
special systematic value has been attached to the presence or absence 
of the embryonic shell (nucleus) in the Gasteropods, which corre- 
sponds with the initial chamber (Anfangskammer) of the shells of 
Cephalopods. 
It may not be out of place to refer here briefly to Dr. Paul 
Fischer’s ‘ Manuel de Conchyliologie,’ noticing first the larger 
divisions which he employs, and, secondly, his grouping of the 
forms comprehended in the suborder J^autiloidea. As to the groups 
that should be embraced in the order Dibranchiata, most zoologists 
and palaeontologists are agreed, there being satisfactory evidence 
(ink-sac, booklets of tentacles, &c.) that many fossil forms belonged 
to this two-giUed order of cuttle-fishes, whose appearance dates 
from the latter part of the Trias. Save in some of its minor divi- 
sions, with which we are not at present concerned, Dr. Fischer's 
arrangement of the Dibranchiata does not depart from that of other 
systematists. The remaining groups of the Cephalopoda are placed 
in two orders — the Ammonea, and the Tetrabranchiata The first 
he finds resembles that of a Dibranch (Argonauta). Eicbwald also (Letb. 
Eoss. Tol. i. p. 1190) placed all the Paleozoic NauHloidea, including Orthoceras, 
Endoceras, Actinoceras, Gomphoceras, Ascoceras, &c., in the Dibranchiata, re- 
serving only four genera — Lituites, Clgmenia, Nautilus, and Goniatites — to 
represent the Tetrabranchiata. 
* Handbuch der Palseontologie, Band ii. Abth. i. p. 354. 
^ It has recentljf been proposed that Owen’s terms Tetrabranchiata and 
Dibranchiata should be abandoned and that the Cephalopoda should be clas- 
sified upon other characters than those of the branchiae. The first suggestion 
of this kind known to me is contained in Dr, Waagen’s well-known work on 
the “ Salt-Eange ” Fossils of India (Mem. Geol. Surv. India — Palaeontologia 
Indica, ser. xiii., Salt-Eange Fossils, 1879, p. 21), where under the division 
Mollusca the author has omitted the word “ Tetrabranchiata ” in the heading 
to his chapter on the Ammonitidae, and inserted the word Order with a query, 
thus “ Order : ?— .” Mr. F. A. Bather (Ann. Mag. Nat. Hist. April 1888, 
p. 302, and ibid. June 1888, p. 423) has suggested the abolition of the terms 
Tetrabranchiata and Dibranchiata, and the division of the Cephalopoda into 
three orders Nautiloidea, Ammonoidea, and Coleoidea (koXcos, sheath), the 
last being his own. But no evidence has as yet been brought forward to prove 
that the fossil forms included by Owen in the Tetrabranchiata were other than 
four-gilled. 
