Genus Graptolithus. 145 



The forms above described do not by any means exhaust the 

 variety 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 radiating branches from a centre, or 

 in tufts joining in a central connecting substance. 



The specimens from the Canadian locality afford further evi- 

 dence 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 examination, 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 comparison of specimens from more southern 

 localities with those of New York, shows a large proportion of 

 new species ; and it now appears probable that the number of 

 American species of Graptolithus previously known (about twen- 

 ty) will soon be increased by an equal number of new ones. 



Locality and Formation. — Point Levy, Hudson River Group. 



Collectors. — J. Richardson, Sir W. E. Logan, and James Hall. 



Since the date of the above communication, great numbers of 

 Graptolites have been added to the Canada collection ; and with 

 an increased number of species, our knowledge of the structure of 

 these animals has been very much extended. Had we at that 

 time possessed all the materials which we now have, the subject 

 might perhaps have been treated in a more natural order by 

 presenting in the first place the more simple forms ; but since the 

 first two plates of the species were then engraved, I follow this 

 note with the descriptions of others of the same character, which 

 have been prepared since that time. 



Graptolithus flexilis. 



Description. — Multibrachiate, bi-lateral ; branches slender, 

 flexile, bifurcating at irregular intervals ; bifurcations of contig- 

 uous branches often opposite, repeated four times within one and 

 a-half inches of the centre, having from thirty-two to forty or 

 more branchlets at the extremities. Substance of branches thin, 

 extremely compressed ; non-celluliferous side smooth or faintly 

 striated; celluliferous side with slight transverse indentations 

 when compressed vertically, and with serratures when compressed 

 laterally; serratures not deep, acute at the extremities, variable in 



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