GKAITOLITES OF NEW YORK, PART 1 729 



d e n t a t u 8 . The same author cites it in his list from Arkansas. Hop- 

 kinson and Lapworth identified a small, more obtusely pointed foim, which 

 they obtained from the Lower Arenig of Kamsey island in Wales, Avitli 

 this species. The latter, if not identical, represents a closely related smaller 

 type. Tyi)ical specimens were collected and described by H. A. Nicholson 

 from the Upper Skiddaw slates (Ellergill beds) which ai-e homotaxial with 

 the beds with I) i p 1 o g r a p t u s d e n t a t u s in the Point Levis and Deep 

 kill regions. Miss Elles also had typical material from the same horizon of 

 the Skiddaw slates for investigation. 



Remarks. This species Avas doubtfully I'eferred by its author to 

 Retiolites. When Nicholson erected the genus Trigonograptus, he assigned 

 R e t i o 1 i t e s e n s i f o r m i s to it, though the genotype was described 

 as having a zigzag virgula, and this form has a straight one. 



It appears that neither in Canada nor in England specimens of such 

 gigantic size were observed as the fragments in the Deep kill beds must 

 have come from. Hall's largest specimen measured nearly 2^ in. (about 

 62 mm), while Miss Elles had a fragment measuring 38 mm. The one repro 

 duced here in figure 3 measures 80 mm. 



Family ci-iMA.coGRAF'Tir>A.E: Freeh 

 cLiMAcoGRAPTus Hall. 1 865 



This genus, which becomes so prominent, both in number of species 

 and individuals, in the highei' zones of the Lower Siluric, is repre- 

 sented by but two species, one of ^vhich, (J . p u n g e n s , though an 

 undoubted Climacograptus, is a very diminutive form, while the othei', 

 C . ? a n t e u n a r i u s, can be referred uul}- with doubt to climacograptus. 



On account of this meager representation of the genus in the lower 

 Lower Siluric, we reserve the discussion of its chaiactei's for the next memoir, 

 in which we shall be ]>etter enabled to illustrate them with the aid of the 

 larger and moi-e typical Ti-enton material. 



