SUPPLEMENT. 
503 
side and laterally flattened, and present a single series of cellules or 
serrations, which are moderately deep, with the serratures acute at their 
extremities; from twenty-four to twenty-eight in an inch. The sub¬ 
stance of the branches, upon the exterior surface near the centre, is 
marked by a depressed longitudinal line, which follows the ramifica¬ 
tions, and gradually dies out as the branches become finally simple, 
when the surface on the same side is smooth or somewhat obliquely 
striated. The disc is smooth exteriorly; and from the centre is a small 
radicle, from which the two sets of branches diverge. 
This species, though in a general manner bilateral and presenting four principal 
branches, is, nevertheless, from the irregular division of these, usually unequal upon 
the two sides; and we find on examination of those figured that they are as ten and 
ten, nine and eleven, eight and nine, ten and eleven, seven and ten, twelve and 
twelve, eight and eight, eight and ten, while the half which is figured (plate ii) 
has eleven rays. 
Locality and formation. These specimens were obtained at Point Levy, opposite 
to Quebec, in a band of bituminous shale separating beds of gray limestone. These 
strata belong to the Lower Silurian series, and are of that part of the Hudson-river 
group which is sometimes designated as Eaton’s sparry limestone, being near the 
summit of the group : they form also the rocks of Quebec. 
Ixiaptolitlms abnormis. 
This species, of which only imperfect specimens have been seen, presents four 
principal branches diverging from the centre, two from each extremity of the vin¬ 
culum, and each one of these bifurcating and branching unequally and at unequal 
distances from the centre. 
The forms above described do not by any means exhaust the varieties presented 
in this collection. With a single exception, however, all the specimens which offer 
any new light in regard to the habit of the Graptolites indicate that the mode of 
growth was in the manner described, in branches radiating from a centre, or in 
tufts joining in a central connecting substance. 
The specimens from the Canadian locality afford further evidence in confirmation 
of what we have elsewhere observed, that, with few exceptions, the species have a 
limited geographical range. This locality has already, after very cursory examina¬ 
tion, afforded eight new species of Graptolites, with one or two species which appear 
to be identical with those previously found in the State of New-York. A compari- 
