﻿296 ARTHRODIRA. 



The type species. Cranial shield ovoid in form, truncated at its 

 hinder border, the outer lateral angles rounded and notched, and 

 the breadth between the latter about equal to the total length ; the 

 anterior two-thirds of the shield gradually arched from side to side, 

 flattened or depressed mesially, the posterior portion of the median 

 occipital plate rising to a broad, low, longitudinal ridge, corresponding 

 to the laterally arched contour of the median dorsal plate of the 

 trunk immediately behind. Median dorsal plate about three times 

 as long as broad, convex in the median line, but highest in the 

 centre, from which point there is a downward slope in every direc- 

 tion, the lateral slopes being most abrupt ; anterior border not ex- 

 cavated ; the sides parallel for more than two-thirds of their length, 

 then converging rapidly into a point with somewhat concave sides. 

 Tuberculations of small or moderate size, often arranged in close, 

 concentric series, especially upon the laterally situated plates. 

 Form. § Loc. Lower Devonian : Campbellton, New Brunswick. 



P. 5474-75, P. 5972. Three imperfect cranial shields, the first 

 about 0*1 in maximum breadth, the second and third dis- 

 playing the linear arrangement of the tubercles. 



Purchased, 1888, 1889. 



P. 5973. Imperfect plate of the form named " ventro-median (?) " 

 by *VVhiteave8, but appearing to the present writer to be 

 the anterior lateral element. Purchased , 1889. 



Phlyctsenaspis anglica, Traquair. 

 [Plate VIII. figs. 5-8.] 



1870. Zenaspis (Cephalaspis) salweyi, E. R. Lankester (errore), Fishes 

 Old Red Sandst. pt. i. (Pal. Soc), p. 55, pi. viii. fig. 4 (? figs. 2, 3), 

 pi. xiii. figs, 17, 18. 



1890. Phlyctrenius anglicus, R. H. Traquair, Geol. Mag. [3] vol. vii. 

 p. 85, pi. iii. fig3. 3, 4. 



Type. Imperfect cranial shield ; Edinburgh Museum. 



Cranial shield ovoid in form, truncated at its hinder border, the 

 outer lateral angles rounded, but not notched, and the breadth be- 

 tween the latter about equal to the total length. Tuberculations 

 of cranial plates relatively very large, but irregular both in size and 

 arrangement, rarely in concentric series ; those of the supposed 

 ventral body-plates exhibiting a more or less definite concentric 

 serial arrangement, and some of the rows very minute. 



Some fragments of this species were assigned by Lankester to un- 

 determined positions in the dermal armature of Cephalaspis salweyi; 



