HISTORY OF RESEARCH. 



(Didymograptvs) . (1) Gr. nitidus, (2) Gr. patulus, (3) Gr. bifidus, 



( I) Gr. indentus, (5) (-/y. extenuatus, (6)Gr.constrictus, 



(7) 6r7'. similis, (8) GV. arcuatus, (9) G^. extensus, 



(10) Gr. pennatulus. 

 (Tetragraptus) . (11) Gr. byronoides, (12) (?r. denticulatus, 



(13) 6'r. quadribrachiatus, (14) 6'r. fruticosus, 



(15) Gr. erwtt/er, (16) Gr. Headt, (17) Gr. ak£«s, 



(18) Gr. Pt>%i. 

 (Dichograptus) . (19) f/r. octobrachiatus, (20) GV. octonarius. 

 (Loganograptus) . (21) Gr. Logani and a variety. 

 (Clonograptu-s) . (22) Gr. flexilia, (23) ^//'. rigidus, (24) ^V. abnormis, 



(25) ^/y. Richardsoni, (20) 6rr. ramulus. 

 Diplograptus . (27) 6V. pristiniformis, (28) Gr. inutilis, (29) G?\ putillus, 



(30) Gr. quadrimucronatus. 

 Climacograptus . (31) 0. antennarius, (32) 0. bicornis, (33) G. typicalis. 

 Dicranograptus . (34) D. ramosus. 

 (Leptograptus) . (35) Gr. flaccidus. 

 Betiolites . . (36) /?. ensiformis, (37) E. venosus. 

 Retiograptus . (38) ft. tentaculatus, (39) R. eucharis. 

 Phyllograptus . (40) P. fypM*, (41) P. ilicifolius, (42) P. anna, 



(43) P. angustifolius. 

 Dendrograptus . (44) D. flexuosus, (45) 2). divergens, (40) 7>. striatus, 



(47) D. erectus, (48) P. diffusus, (49) D. gracilis. 

 Callograptus . (50) G. elegans, (51) G. Salteri. 

 Dictyonema . (52) D. irregularis, (53) D. robusta, (54) />. Murrayi, 



(55) 7>. quadrangularis. 

 Ptilograptus (56) P. plumosus, (57) /'. Geinitzianus. 



Thamnograptus . (58) T. anna. 

 (Monograptus) . (59) Gr. Clintonensis. 



In his introductory chapters Hall devotes various sections of his work to the 

 consideration of such matters as the structure, method of reproduction, and mode 

 of existence of the Graptolites. Such of his views as were new to the science of 

 the time may here be briefly summarised. 



Structure. 



The Radicle. — This was the name employed by Hall for the basal spine, initial 

 spine, or " initial point" of the Graptolite. He admits that in those species with a 

 single row of cellules it may have served as a temporary organ of attachment in the 

 earlier period of its growth, " though all the evidence is opposed to this view." In 

 Retiograptiis, however, it " is only a broken process of attachment of the individual 



