No. 186.J 51 



Fig. 3 shows the central portion or radix, with the bases of the branches ; 

 while two of these are shown in their extension, laterally compressed and 

 showing the serratures. The entire length of some of these branches is about 

 seven inches. 



Graptolithus logani. 



Frond composed of numerous branches nearly equally disposed on two 

 sides of a central connecting stipe, and each again subdividing nearly 

 equally ; after which they bifurcate, always near the base, with greater 

 or less regularity : connecting membrane thin, composed of the same 

 substance and continuous with the branches, extending from the centre 

 to some distance beyond the bifurcations. The branches, after the third 

 bifurcation, become marked on the inner side by a row of cellules, and 

 along the centre by an abruptly impressed line which follows the di- 

 varication of the branches : cellules minute, not prominent towards the 

 base of the branches, being compressed vertically, and appearing like a 

 double series with a central depressed line, becoming developed as they 

 recede from the base. The branches beyond the disk are turned on one 

 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 substance 

 of the branches, upon the exterior surface near the centre, is marked by 

 a depressed longitudinal line, which follows the ramifications, and gra- 

 dually dies out as the branches become finally simple, when the surface 

 on the same side is smooth or somewhat obliquely striated. The disk 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 grey 

 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. 



Graptolithus abnoHmis. 



This species, of which only imperfect specimens have been seen, presents 

 four principal branches diverging from the centre, two from each extremity 

 of the vinculum, and each one of these bifurcating and branching unequal- 

 ly and at unequal distances from the centre. 



