HISTORY OF RESEARCH. xli 



The remaining forms, all of which were new to science, are (4) Gr. octo- 

 brachiatus, (5) Gr. octonarius (Dichograptus) ; (6) Gr. quadribrachiatus, (7) Gr. 

 crucifer, (8) Gr. bryonoides, (9) Gr. Headi, (10) Gr. alatus, (11) Gr. fruticosus, (12) 

 Gr. denticulatus (Tetragraptus)'; (13) Gr. indentus, (1 t) Gr. nitidus, (15) Gr. 

 bifidus, (16) Gr. patulus, (17) Gr. similis, (18) Gr. extensus (Didymograptus) ; (19) 

 Gr. pristiniformis (Diplograptus) ; (20) Gr. ensiformis (Betiolites, Hall); (21) Gr. 

 tentaculatus (Betiograptus, Hall). 



In addition to these, Hall describes three species of a remarkable four- 

 rowed type, viz. (22) P. typus, (23) P. ilicifolius, and (24) P. angustifolius. 

 For these he suggests the new generic name of Phyllograptus. He explains the 

 structure of these forms, and shows that they consist of "four semi-elliptical parts 

 joined at their straight sides." 



Hall was well aware that the exact number of branches did not constitute either 

 a generic or specific character in some of his new forms, for he notices a specimen 

 of Gr. octobrachiatus with only seven branches, and a Gr. Logani with nine. 



The genera, Thain.itoi/ruptn.i and Dendrograptus ' are briefly referred to, and he 

 also describes a new genus which he calls Plumulina, of which he gives two 

 species, (25) P. plumaria and (26) P. gracilis. 



Hall also figures some Graptolite stipes with reproductive cells. As the 

 question of the reproduction of the Graptolites is entered into in greater detail by 

 Hall in his ' Graptolites of the Quebec Group ' (1865), the discussion of his results 

 will be referred to later. 



He disagrees with Barrande's view that the narrower end is the newest part 

 of the polypary, and shows that the origin of the stipe in some of the Canadian 

 forms renders this untenable. In other respects he does not add much to our 

 knowledge of the structure of the Graptolites. Referring to those forms which 

 have cells on two sides (JDiplograpsus) , he is '" disposed to believe that they may 

 have been simple from the base," though the bifurcated appearance of D. bicomis 

 offers objection to this view. 



As regards the mode of life of the Graptolites, Hall is somewhat in favour of the 

 theory of their having been free floating animals ; for, as he points out, "in many 

 specimens there is no evidence of a point of attachment or radix, and they have 

 much the appearance of bodies floating free in the ocean." 



He notes how strongly the Graptolites simulate the Palaeozoic Bryozoa in mode 

 of growth, though they differ essentially from all of them, not only in form, bu.1 

 in the arrangement of their cellules, in the nature of their substance, and in the 

 structure of their skeleton. 



1 The actual description of Thamnograptus was not published until 1859 (Pal. New York. vol. iii, 

 Suppl.). Dendrograptus, though named in 1857, docs not seem to have been fully described until 

 18(35 (G-raps. of Quebec Group). 



