MINERALS AND GEOLOGY OF CANADA. 517 
Palasterina.—Five rays, with intermediate connecting area. 
P. stellata, more or less regularly pentagonal. 
P. rugosa, dorsal plates in part stelliform (ventral aspect unknown.) 
Petraster—Connecting area very slightly developed. Large marginal 
plates. P. rigidus, (characters imperfectly known.) 
Stenaster.—No connecting area. Rays without spines or overlapping 
plates. SS. Salteri, rays comparatively broad. 
S. pulchellus, rays long and narrow. 
Teniaster—No connecting area. Rays narrow, covered in part with 
spines, and with their outer, or adambulacral, plates partly over- 
lapping. JZ. spinosus; 7’. cylindricus, (The latter of these is 
apparently the larger and more robust species of the two, but 
otherwise the characters are much alike). 
In addition to these forms, small and more or less imperfect specimens of 
Asterida, probably referable to Hall’s genus Paleaster, are occasionally obtained 
from the Niagara limestone of the Upper Silurian Series. 
6. Ophiurida.—The star-fishes of this Order differ from the 
Asterida proper, in having their arms or rays quite distinct from the 
central visceral-cavity. With the exception of a doubtful fragment 
from the eastern Post-Tertiary deposits (see Part V.), no examples 
have as yet been noticed in Canadian rocks. 
7. Euryalida.—In this Order, the arms and stomach are also 
distinct, but the body is only partially covered by calcareous plates. 
No fossil representatives.* 
8. Echinida.—This is an important Order, but fossil representatives, 
are all but unknown below the Mesozoic rocks, and none (with the ex- 
ception of a modern form in the Post-Tertiaries of Beauport, see Part 
V.) are of Canadian occurrence. The echinids, of which the modern 
*‘sea-ege”’ or ‘“sea-urchin”’ may be taken as a type, have no arms. 
The body is hemispherical, oval, cordiform, &c., and covered by a 
calcareous test or shell, composed of polygonal plates joined at their 
edges. Some of these plates, in radiating areas termed “ ambulacra,” 
are perforated for the passage of retractile respiratory tubes. The test, 
moreover, is covered by moveable calcareous spines (which fall off 
after the death of the animal) ; and it has always two openings, one 
of which, the mouth, is invariably situated on the under side of the 
body. In existing seas these forms are exceedingly abundant, and 
they appear to have been equally numerous in the seas of the Caino- 
zoic and Mesozoic ages (see Table of Formations, page 453, above). 
* The Protaster of E. Forbes .is now referred to the Ophiurida. 
