BY JOHN MITCHELL. 485 



tubercle at the spot where it crosses, and a single median one 

 behind the axis. The posterior pleural ridges are prolonged into 

 short, recurved, equidistant, and subequal spines, projecting 

 beyond the margin. (In one specimen there seems to be a 

 median spine behind the axis. In another immature example 

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

 whole pygidium). Surface of pygidium rather coarsely tuber- 

 culated: the posterior ridge of each pleura bears 4-5 tubercles, 

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

 each 5-7 tubercles." 



" Dimensions: — 



Length of head-shield ... ... ... .. 8 'Omni. 



Width of head-.'^hield ... ... ... ... 4'omm. 



Length of pyoidiuni ... ... ... ... 2*5 mm. 



Width of pygidium 4 "0 mm. 



For affinities, see op. cit. 



To quote Reed further, he remarks that " McCoy gave as 

 generic characters the circle of tubercles round the eyes and pair 

 of large tubercles at the front end of the glabella, but these may 

 well be considered as of lower classificatory value, and likewise 

 the relatively greater length of the glabella as compared with 

 the European species. It does not, however, seem possible to 

 regard tlie peculiar pygidial characters in the same light, though, 

 as Vogdes (Trans. Acad. So. St. Louis, Vol. v, (1892), p, 617) 

 .says, we have many other genera of trilobites with spinose and 

 non-spinose representatives. The fewer number of segments in 

 the p\'gidium, and the rai.sed spinigerous boi'der separate it from 

 all the European forms. " 



" The genus or subgenus Phcetonides, as now understood, is 

 partly distinguished for analogous reasons from the typical 

 Proetus; and it seems open to question whether the European 

 species of Brachymetojnis should not be regarded as constituting 

 a distinct group or subgenus for which the name of Brachymeto- 

 pina may be suggested." 



Personally, I do not think that pygidial characteristics alone 

 are sufficient grounds upon which to found even a 5^ubgenus 



Loc. and Hor. — Dunvegan, Burragood, and Glen William, 



36 



