CYRTOGRAPTUS. 



605 



Figs. 351 a-^c.-^HojmpiKs m«;t;u " brancliGS " are individual colonies normally des- 

 -r-, tined to an independent existence, but which have 



remained so far permanently attached to the parent. 

 Thus, the whole compound colony, or colony of 

 colonies (its general form excepted), recalls in a 

 sense the " synrhabdosome "^ of Ruedemann, while 

 the sac-like bodies recall the " graptogonophores " ^ 

 of Nicholson. 



In order, therefore, to avoid restricting ourselves 

 to any particular theory, we here employ in our 

 diagnoses of the various species in the present group 

 the conventional term " dadiiim " for each of the 

 so-called "branches," and tlie term " saccoid" ior 

 each of the initial sac-like expansions. 



The difference in the appearance of the thecse 

 on the stipe and cladia is mainly an apparent one, 

 and is due to difference in curvature. In the spiral 

 portion of the polypary, the thecal, being on the 

 convex side of the curve, are stretched, whereas in 

 the distal portion of the stipe and on the cladia the 

 tliecse are, as a rule, on the concave side, and are 

 therefore compressed, thus tending to show a greater 

 degree of overlap. 



In some species the spiral enrolling of the stipe 

 is considerable (C Murclusoni), while in others it is 

 but slight {C. Linnarssoh!). 

 The following species are included in this genus : Gyvtog. MurcJdsoni, C. 



Lundgreni, C. rigidua, G. symmetricns, G. hamatas, G. Linnarssoni, G. Grayi, G. 



Garruthersi. 



— c. — Three fragments, showing the 

 various appearances presented by 

 the " sarcoid " and the first theca of 

 the " cladium." Pencerrig, Builth ; 

 Wenlock Shales (zone of C. Murchi- 

 soni). Coll. EUes. 



Cyrtograptus Murchisoni, Carruthers. Plate LI, figs. 3 a — c. 



1867. Cyrtograpsus Murchisoni, Carruthers in Murcliison's Siluria, Fossils 90, fig. 1, p. 541. 



1868. Cyrtograpsus Murchisoni, Carruthers, Geol. Mag., vol. v, p. 127, pi. v, fig. 17. 

 1883. Cyrtograptus Murchisoni, Tullberg, Sk^ues Grapt., ii, p. ;}5, pi. iv, figs. 9-11. 



1900. Cyrtograptus Murchisoni, Elles, Quart. Journ. Geol. Soc, vol. Ivi, p. 409, pi. xxiv, fig. 6. 



Polypary robust, several square cm. in extent ; stipe arcuate, with spirally 

 enrolled proximal portion, which widens slightly but quickly until the 



1 Kuedemann, Grapt. New York, 1904, p. 483. 



2 Nicholson, Geol. Mag., 1866, vol. iii, p. 489. 



