556 NEW YORK STATE MUSEUM 



(2) OEAPTOLITES DBRIVED FROM 0L0N0GKAPTU8 



(/) * Dlchograptus octonarias 

 Tetragraptus aerra 

 * Didymograptus arcuatus 



{g) Loganograptus logani 



Dichogra/ptus octohrachiatus 



Tetragraptus quadrihrachiatus 

 Didymograptus extensus 

 (A) * Tetragraptus headi 

 Didymograptus jpatulus 



These groups can readily be arranged into genealogic trees or diagrams, 

 as has been done by Miss EUes, the first of these having Dictyonema and the 

 (Others Clonograptus as their basal form. 



The forms which are constituents of the New York fauna are printed 

 here in italics and those not reported from here, but found in Canada, are 

 marked by an asterisk. This arrangement readily shows that the ancestral 

 species of Bryograptus are foreign to this continent ; but, on the other hand, 

 some forms have been cited in the lists which have not yet been found in the 

 Skiddaw slates. This would be expected in a class which, like that of the 

 graptolites, has not developed in a small restricted area, but is of world-wide 

 distribution, and the complete phylogeny of which could hence be obtained 

 only by a comprehensive study of all the contemporaneous forms. 



A closer inspection of the lists cited above demonstrates that there 

 still e.xist considerable gaps and differences between some of the forms, which, 

 for instance, between Bryograptus ramosus var. cumbrensis and 

 Tetragraptus fruticosus, are so great — not only in general appear- 

 ance but also in the character of the thecae — that a derivation of the latter 

 from the former without existing intermediate forms is still hypothetic. 



On the whole, however, the study of the succession and morphology of 

 the Dichograptidae of the Deep kill fauna not only has corroborated the view 

 of the British authors on the probable phylogeny of these forms, but has also 

 furnished a considerable number of additional similarities between different 

 species and genera, which are enumerated here : 



(1) The series leading to Tetragraptus fruticosus is continued 

 in the next horizon byT.clarkei. 



The relation of these two species is discussed under the latter [p.653], 

 and it is stated there that T. clarkei is a later, interesting derivative from 



