MINERALS AND GEOLOGY OF CANADA. 19 
Family 1., Navrin1p2.—Septa with entire or slightly sinuous mar- 
gins. Siphunele, variable. 
Sub-Hamily 1, Gomphoceratide.—Aperture of shell partly 
closed, or much contracted. 
Sub- Family 2, Orthoceratide, or Nautilide proper.—Aper- 
ture more or less open. 
Family I1., AMMonir1pm.—Septa prominently lobed. Siphuncle 
external,” or along the apparent back of the shell. 
Sub-Hamily 1, Goniatide.—Septa angulated, 7. ¢., with 
angular lobes. 
Sub- Family 2, Ceratide.—Septa lobed and denticulated. 
Sub-Family 3, Ammonitide proper.—Septa foliated. 
The Ceratide and Ammonitide proper are entirely restricted to 
rocks of Mesozoic age, and are consequently unknown among Cana- 
dian fossils. (See the Table of Formations given at page 453 of 
Vol. VI., and also those of Canadian occurrence on the succeeding 
page). The sub-families of the Gomphoceratide, Orthoceratide, 
and Goniatide present Canadian examples; but those belonging 
to the first and last of these sub-families, are few in number and 
of comparatively rare occurrence; and even the Orthoceratide, 
though rich in examples, are confined, with us, to a small number of 
genera. It is not necessary, therefore, in describing these forins, to 
adhere to any close system of classification, more especially as the 
fragmentary or otherwise imperfect condition in which the fossil 
cephalopods of the lower rocks so generally occur, forbids in many 
instances the strict application of definite structural characters. 
This understood, our Canadian genera may be conveniently described 
in the following order: Orthoceras (including G'onioceras, &c., as 
explained below), Cyrtoceras, Phraqmoceras (belonging to the first 
sub-family, but placed here, for convenience, as allied by form to 
cyrtoceras), Litwites, Nautilus, and Goniatites. Other genera, enu- 
merated by paleontologists, and occurring with us, are distributed 
under one or more of these types.* 
* Many of the genera hitherto established for the Tetrabranchiate Cephalopods can only 
be regarded as provisional. Characters until recently considered of generic value (aud on 
which distinct genera have been founded by Pictet, D’Orbigny, Hall, and other paleeontolo: 
gists of authority), are now shewn to be more or less inconstant, and consequently of un- 
certain application. The siphuncle in its form and position, as regards at least the types 
with simple septa, appears more especially to be acharacter of this kind; but it may be 
questioned whether tho mere shape of the shell, although a readily observable character in 
most instances, and hence a convenient one, is actually of any greater value. It would 
seem, for example, that relations quite as close must have obtained between an orthocerag 
with ordinary siphuncle and a slightly curved cyrtoceras—as between the former and an 
orthoceras (or endoceras) with a laterally-situated siphuncle of large size and more or legs 
aberrant structure, 
