A POPULAR EXPOSITION, ETC. 17 
A POPULAR EXPOSITION OF THE MINERALS AND 
GEOLOGY OF CANADA. 
BY E. J. CHAPMAN, Ph. D. 
PROFESSOR OF MINERALOGY AND GEOLOGY IN UNIVERSITY COLLEGE, TORONTO. 
PART IV. 
(Continued from Vol. VII. page 121.) 
The various classes and orders of molluscous animals, with the ex- 
ception of the class Cephalopoda, were described in reference to their 
fossil relations, in the last article of this series. In the present article 
we resume and complete our rapid sketch of the more prominent 
features of Canadian Paleontology, bringing Parr IV. of our Essay 
toaclose. The concluding portion, or Part Y., of the series, em- 
bracing a general view of our rock groups, in their topographical, 
economic, and other relations, will appear in an early number of the 
Journal, 
CrpHatopopa.—The Cephalopods are the most highly organised 
representatives of the molluscous type. They possess a distinct 
head, furnished with large eyes and with a central mouth. The 
latter contains a pair of horny jaws or “ beaks,’ (somewhat resem- 
bling, although in reversed position, the beaks of a parrot), and is 
surrounded by eight or ten arms, or by a greater number of tenta- 
cles, serving partly for locomotion, but chiefly for prehensile pur- 
poses. It is from the possession of these arms or tentacles, viewed 
as organs of locomotion, that the class derives its name of Cephalop- 
oda or ‘‘head-footed.” Its species are entirely marine. The 
Nautilus, the Argonaut or “Paper Nautilus,’ and the Sepia or 
Cuttle-fish, may be cited as characteristic living types. 
The Cephalopods fall into two orders or leading groups, viz. : 
(1.) Zetrabranchiata or Tentaculifera; and (2.) Dibranchiata or 
Acetabulifera. The tetrabranchiate or tentaculiferous cephalopods 
possess four branchie or organs of respiration, numerous simple or 
unarmed tentacles, and a many-chambered shell. The dibranchiate 
or acetabuliferous cephalopods have only two branchiz, and eight or 
ten arms; but the latter are provided on the inside with special 
organs of prehension in the form of acetabula or “ suckers.” These 
forms also possess a so-called “‘ ink-bag,”’ or internal sack, containing 
a dark fluid secretion which the animal can eject into the surround- 
Vou. VIII. c 
