MINERALS AND GEOLOGY OF CANADA. 513 
Numerous stem-fragments of crinoids occur throughout our Silurian 
and Devonian rocks, but entire or even tolerably perfect forms are 
exceedingly rare. As the character of the 
stem differs frequently in the same species, 
and in different parts even of its own length, 
and ismore or less alike again in different spe- 
cies, these fragments can only be described 
as “crinoid stems.” Fig. 83 represents 
a piece of arenaceous shale, from below the 
Drift clay of Toronto, covered with portions 
ofcrinoid stems, some being seenin transverse 
sections, whilst others are shewn longitudi- 
Fig. 83. nally. This shale belongs to the Hudson 
River Group of the Lower Silurian Series (see Part V.) 
Owing to this fragmentary condition of our Canadian examples 
generally, and to the great rarity of perfect or determinable forms, it 
is unnecessary in an essay like the present (and would indeed be 
useless where we are obliged to restrict the number of our engravings) 
to attempt descriptions of genera and species. The crinoids of our 
Lower Silurian strata will be found described in great detail by Mr. 
Billings, in the fourth Decade of ‘‘ Canadian Organic Remains.”’* Of 
the species met with in our other formations, no complete record has 
yet been published. 
2. Blastoida.—The forms placed in this Order have been separated 
of late years from the Crinoids proper. They present an oval or 
globular body, (the calyx) composed of several series of plates, and 
having at the summit five “ambulacral areas” or rays, in the shape 
of a star, furrowed down the centre of each ray, and striated across. 
These are thought to have supported delicate tentacles, but no arms 
have been discovered. The body was fixed to the sea-bottom by a 
short, jointed stem. The order contains but few genera. The genus 
* In further illustration of the inutility of entering into descriptions of these forms in the 
present place, it may be observed that, of several species described and figured by Mr6 
Billings, only single specimens are known. We have therefore thought it advisable to 
restrict, for the greater part, our limited number of engravings to representations of char- 
acteristic or commonly-occurring corals, brachiopods, lamellibranchiates, gasteropods, cepha- 
lopods, and trilobites. 
