(JRAPTOLITBS OF XEAY YORK, PART 1 



673 



corresponding to the Tetragraptus beds of the Deep kill, in the Middle Arenig 

 of St David's, in the Lleyn peninsula of Wales and in Shropshiie. In Scandi- 

 navia the species does not appear to have as j^et been clearly recognized ; 

 Herrmann \loc. cii.] cites it as "doubtfully in Phyllograptus shales, Norway." 

 Barrois describes D. n i t i d u s as common in the graptolite schists at 

 Boutoury near Cabrieres ; and the younger Etheridge ]-ecords it from Castle- 

 maine in Victoria, Australia, but his 

 identification is doubted by Lapworth, 



Elles and Wood. ,.• «« r.-, 



Fifi'. 69 D 1 dymo si'upt us nitidiis Hall sp. 

 7") 7 m • j:„1 ,% Frafiinent of branch, showing- ditterent asi)ects of 



MemarkS. Ine primary aiSk is thec.ie due to ditterent direction ut compression. 



Deep kill, xo.ih 



observable in a considerable number of 



specimens. It is found close to the apex of the sicula, so that the latter 

 appears to have been as a rule attached by only a very short nema and even 

 without the intercalation of such, as in figure 3. I have not observed aii}^ 

 disks on larger rhabdosomes, but this is possibly due to the fact that I did not 

 find any larger specimens so isolated and unencumbered by other fossils on 

 smooth surfaces that I was able to distinguish these delicate appendages. 



This species approaches D. p at u 1 u s on one hand, and D. e x t e n s u s 

 on the other, and it is difficult to assign some forms to one of the three. This 

 is specially true in regard to the differentiation of the closely allied species D. 



n i t i d u s and D. p a t u 1 u s. The closer arrange- 

 ment of the tliecae in D. n i t i d u s and the 

 greater width of the branches of D. patulus 

 are the principal distinctive characters. The 

 greater number of thecae \\'ithin a certain space 

 and the more i-apid widening of the branches Avill 

 also distinguish the tj^pical D. n i t i d u s from D. e x t e n s u s. 



A fcNv of the specimens Avhich we had to refer to this species [fig. 5] 

 greatly surpass in length and width of the branches attained the examples 

 described from Canada and Great Britain. At the same time they show just 

 a little looser ari'angement (11 in 10mm) than the typical D. nitidus, 

 but still a greater number of thecae in a unit than D. extensus and D. 



Fig-. 70 Didymog-raptus ni- 

 tidus Hall ^p. Fragment of branch. 

 The periderm is lost and the form of 

 the coenosarcal cavities is shown by 

 the pyrite flUing. Deep kill. .\- 7 



