F. R. Cowper Heed — On Brach^metopus. 195 



^eems to be a median spine behind the axis. In anotber immature 

 example the anterior two or three pairs of spines are half as long 

 as the whole pygidiura.) Surface of pygidium rather coarsely 

 tuberculated ; the posterior ridge of each pleura bears 4-5 Jubercles, 

 and the anterior ridge 5-6 smaller ones. The axial rings bear each 

 5-7 tubercles. 



Dimensions. mm. 



Length of head-shield ... 3-0 



Width of head-shield 4-5 



Length of p j gidium ... ... ... 2-5 



Width of pygidium 4-0 



Kemaeks. — De Koninck ^ published a fuller description of this 

 species than McCoy, but the figures differ in some respects from 

 those given by the latter and from the type-specimens, though the 

 differences are only of minor importance. As stated in the text by 

 De Koninck and indicated in the figure, the lateral lobes of the 

 pygidium possess seven pairs of pleuras, but the last pair is very 

 small and short ; the margin also possesses seven pairs of spines, 

 but no median one behind the axis. In McCoy's figure there are 

 eight pairs of spines and no median one. De Koninck states that 

 the axis of the pygidium consists of 17 segments, but his figure 

 only shows 7, while that of McCoy shows 10. In De Koninck's 

 figure of the head-shield the genal angles ai-e produced backwards 

 and pointed, instead of being nearly rectangular and provided with 

 spines ; the glabella, also, is made broad and subtriangular, instead 

 of narrow and subcylindrical as in the types ; and the basal furrows 

 or lobes are neither mentioned in the description nor indicated in 

 the figures. 



Affinities. — McCoy remarks (op, cit.) that " the greater size 

 of the glabella and its being widest at the base will distinguish the 

 head from that of Phillipsia \^Brachymetopiis^ Maccoyi (Portk.), and 

 the granulation extending entirely across the segments and the 

 «pinose margin will distinguish the pygidium from that of 

 P. [-B''.] discors (McCoy)." It may, however, be mentioned that 

 the number of segments in the pygidial axis of the latter is much 

 greater, being 17. McCoy also says that Br. Maccoyi "is at first 

 sight difficult to distinguish specifically from the Australian species," 

 but the pygidium of the former has 15 segments in the axis, and 

 no spines on the margin, as well as no distinct border with regularly 

 arranged tubercles. In the other British species there are likewise 

 no marginal spines nor border, and all have a greater number of 

 pygidial segments, Br. ouralicus having 17 and Br. hiberniciis 11. 



McCoy gave as generic characters the circle of tubercles round 

 the eyes and the pair of large tubercles at the front end of the 

 glabella, but these may well be considered of lower classificatory 

 value, and likewise the relatively greater length of the glabella 

 as compared with European species. It does not, however, seem 

 possible to regard the peculiar pygidial characters in quite the same 

 ■light, though, as Vogdes- says, we have many other genera of 



1 Foss. Palfcoz. Nonv. Galles, 1877, p. 352, pi. xxiv, figs. 10a, b, c. 

 • Vogdes: Trans. Acad. Sc. St. Louis, vol. v (1892), p. 617. 



