MINERALS AND GEOLOGY OF CANADA. 25 
of an inch across the opening, has been described by Mr. Billings 
from the Chazy limestone of the Lower Silurian Series (Canadian 
Nat., vol. iv., page 470). Other genera of cephalobranchiate anne- 
lids form a protecting tube or sheath of fragments of shells or grains 
of sand (Terrebella, Sabella) ; but our rocks have not yet offered any 
examples of these. 
CrrrHoropa.—The cirrhopods form a small group of marine ani- 
mals, sedentary in their adult condition, and more resembling mol- 
lusks at first sight than members of the articulated series. They 
secrete an external many-valved shell, and possess a number of delicate 
plume-like cirrhi, or so-called “arms,” capable of protrusion beyond 
the shell, and of thus creating currents in the water, by which food is 
brought within the creature’s reach. There are two more or less 
distinct types: pedunculated and sessile cirrhopods. In the former, 
to which the well-known barnacles belong, the animal is attached, 
head downwards, to ships’ bottoms, pieces of floating timber, &c., by 
a kind of semi-corneous stem; whilst in the latter, typified by the 
balanus or “sea acorn,”’ the shell is fixed directly by its base to rocks 
and other sub--marine bodies, or to such as lie between the tide-marks.* 
Fig. 136 represents a group of several balani, to shew the general 
form of the shell. Fragments of one or two 
species occur in our Post-Tertiary or compara- 
tively modern deposits, at Beauport and else- 
where in Hastern Canada (see Parr V.); but no 
cirrhopods are met with in our lower rocks. The 
balanide, indeed, appear to date only from the 
Tertiary age, although the anatifide or pedunculated forms exhibit 
representatives as low down as the Jurassic series, and perhaps in still 
older deposits. 
Crusracea.—This important class, abundant at the present time 
in genera and species, is sub-divided into a considerable number of 
Orders; but, of these, two only, embracing the Cyproids and the 
Trilobites, present examples of common occurrence in Canadian rocks. 
The higher and more typical forms of the crustaceans—the Deca- 
pods—comprising the various lobsters, crabs, and other allied species— 
offer no representatives below the Carboniferous formations. 
Fig. 186. 
* The balani, though usually fixed to stationary bodies, are sometimes, like their cousins 
the barnacles, fated to a more or less migratory life. We carried off surreptitiously from a 
public dinner table, a short time ago, the beak or projecting part of the head-covering of a 
large lobster, to the extremity of which a full grown balanus was attached. The specimen 
may be seen, by the curious in such matters, in the Museum of the Toronto University. 
