634 NEW YORK STATE MUSEUM 



DicHOGRAPTus Salter. 1863 (modified) 



The genus Dichograptus was erected by Salter [1863, p.l39] and 

 defined as follows : " Frond repeatedly dichotomous from a short basal 

 stipe into 8, 16, 24 or more branches, each with a single row of cells." 

 His Dichograpsus aranea, being the first form figured, would be 

 the genotype, but, as it is a synonym of Hall's Graptolithus octo- 

 brachiatus, the latter becomes the type. 



Later writers have successively separated groups of species under new 

 generic terms from the assemblage of forms embraced by Salter's definition, 

 and, following Lapworth's and Nicholson's example, restricted the genus 

 Dichograptus to forms with eight branches of the third order, with 

 D. octobrachiatus as genotype. Also, Hall used the term in this 

 restricted sense [1863, p.226]. EUes [1898, p.483] and Elles and Wood 

 define Dichograptus by the restriction of the formation of branches to that 

 of three orders [see under Loganograptus, p.630], which gives eight branches 

 as the maximal number. 



As there are several species (D . octobrachiatus Hall, D. octo- 

 n a r i u s Hall and D. separatus Elles) known to have normally branches 

 of three orders, this stage seems to be important enough to be designated 

 by a separate name. For this reason we also use here the term Dichograptus, 

 applying it in its restricted sense. The fact, however, that D. separatus 

 belongs clearly to another evolutionary series than the other two species here 

 cited [see Introduction, p.559], indicates that the group is of polyphyletic 

 origin and not of generic value. 



Dichograptus octobrachiatus Hall (sp.) 



Plate 8, flgrures 1-7 ; plate 9, flgTires 1, 2 



Graptolithus octobrachiatus Hall. Geol. Sur. Can. Rep't for 1857. 1858. 



p.l22 

 Dichograpsus aranea Salter. Quar. Jonr. Geol. Soc. 1863. 19:137, 



fig.9, 10 



