276 NEW YORK STATIC MUSEUM 



names, though he had pointed out in 1865 that Emmons's species is " appar- 

 ently a part of an individual of Graptolithus gracilis, or some 

 similar species." Hall's name was generally accepted ; the just application 

 of the law of priority requires, however, the resurrection of Emmons's older 

 name. 



As to the mode of bifurcation in Nemagraptus, I do not find an} - notes 

 in the literature other than that the secondary branches are thrown off of 

 the main stipes opposite the apertures of the thecae. A few specimens of 

 N . gracilis allow, by a slight infiltration of the basal parts of the thecae 

 an insight into the mode of bifurcation [see fig. 191]. In these the new 

 stolonal theca is seen to originate close to the aperture of the mother theca 

 (about one fifth of the latter's length from the aperture) and to grow in the 

 axial direction of the mother theca as far as the aperture 

 of the latter, where the first theca of the secondary branch 

 is produced from it. At this point both the mother and 

 daughter theca change their direction, but so that the 



Fig. 191 Nemagraptus. . , 1-1 "1 t • l 



gracilis (Hain. Portion former diverges but a little to one side, conforming- to the 



of specimen from the Nor- *-> ° 



curvature of the main stipe, while the latter diverges so 

 much (complement of angle of other) that both together form a right 

 angle. It appears hence that N. gracilis, and presumably the whole 

 genus, conform to the principle enunciated by the writer for Goniograptus 

 [1902, p.583], viz, that "the bifurcations of the branches throughout the 

 rhabdosome take place in the same manner as the formation of the main 

 stipe by the sicula, viz, by the successive budding of two thecae, the second 

 of which buds from the first, and both of which, assuming diverging direc- 

 tions, determine the direction of the branches." This principle quite 

 apparently holds true for all Graptoloidea Axonolipa. 



Figure 191 shows that the mother thecae of the secondary branches in 

 N. gracilis bud alternately on opposite sides of the basal parts of the 

 stolonal thecae, a feature which before has been pointed out by the writer 

 [1904, p. 564] in the discussion of the phylogenetic relations of SigmagraptUS 

 and Nemagraptus. 



