﻿272 MIL F. E. C. REED ON THE FAUNA OF [May I9IO, 



Hamilton Beds of North America ; or we may interpret the facts 

 as indicating that Chasmops appeared at an earlier date in the 

 western than in the eastern parts of its faunal province. 



The slight intermixture of forms belonging to more than one 

 horizon of the Baltic Province (as limited by Freeh) may partly be 

 due to different rates of migration of the various elements of the 

 fauna, some moving more slowly than others. But there can be 

 no doubt that the general faunistic facies of the Glensaul, Tour- 

 makeady, and Shangort Beds is Scandinavian, and that the whole 

 assemblage of species indicates the lower part of the Ordovician. 



In what manner this Irish fauna was separated during its 

 existence from that of the British seas is a matter of speculation ; 

 but we need not call into existence a rock-barrier or land-mass to 

 account for the difference in character. It is also noteworthy that 

 members of the westernmost part of the Atlantic Province made 

 their way into this Irish sea : for Bathyurellus and Bathyurus are 

 typically Canadian genera, and have not previously been recorded 

 from the British Isles or from any part of Europe. 



Ili^enus weaveet, Eeed. 



In my previous description l of this species no mention was made 

 of terrace-lines across the posterior portion of the middle shield ; 

 but, in the numerous specimens from limestones 97 & 155, they 

 are well preserved, and twelve to fourteen nearly continuous, gently 

 arched, fairly regular and equidistant, raised, thread-like lines are 

 seen to cross the glabella between the axial furrows, and extend 

 forwards over an area of about a third of the length of the head- 

 shield. The terrace-lines in /. esmarlci, Schloth., to which this 

 species has been compared, are more strongly curved and set more 

 widely apart. 



Niobe sp. (PI. XXII, figs. 3 a & 3 6.) 



An imperfect fragment of a pygidium which occurs in the 

 limestone of Glensaul (155) deserves special notice, as it must be 

 referred to the genus Niobe. 



It seems to resemble in general characters Niobe insignis, Linrs. 2 , 

 although the number of pleurae on the lateral lobes is less, being only 

 tour. Prof. Brogger 3 regards Billings's Asaphus morrisii^ from 

 Newfoundland, as the American representative of this Norwegian 

 species. The small species Niobe obsoleta, Linrs., may be compared. 



1 Quart. Journ. Geol. Soc. vol. lxv (1909) p. 142 & pi. vi, figs. 1-3. 



2 J. G. O. Linnarsson, ' Om Vestergotlands Cambriska & Siluriska 

 Aflagringar' K. Svenska Vetensk. Akad. Handl. vol. viii, no. 2 (1869) p. 75 & 

 pi. ii, fig. 36 ; W. C. Brogger, ' Die Silurischen Etagen 2 & 3 ' Christiania, 

 1882, p. 66 & pi. iv, figs. 1 a-d. 



3 ' Verbreitung der Euloma-Niobe Fauna ' Nyt Mag. Naturvidensk. vol. xxxvi 

 1898) p. 226. 



4 E. Billings, ' Palaeozoic Fossils of Canada ' vol. i (1865) p. 272 & fig. 257. 



