PROETUS GIRVANENSIS. 75 



to cut posterior margin of head at about 30° halfway between glabella and 

 genal angles. Free cheeks triangular, gently convex, bent down strongly ; 

 genal angles produced into short tapering pointed spines, reaching back to about 

 fourth thoracic segment. Eyes large, prominent, subreniform, more than one 

 third the length of glabella and situated very close to it ; elevated on distinct 

 base with narrow rim and strong furrow below. 



Thorax of ten segments, longer than head. Axis convex, tapering 

 gradually to pygidium, broader than pleura; ; axial rings with minute median 

 tubercle and well-developed lateral nodules on each (particularly well shown in 

 casts). Pleurse strongly bent down beyond fulcrum, but very slightly curved back ; 

 strong diagonal pleural groove ; extremities slightly recurved, pointed, with broad 

 articulating surface on anterior margin for rolling up. Fulcrum weak, situated at 

 about half the length of pleurae. 



Pygidium broadly semicircular. Axis convex, prominent, occupying middle 

 third and extending about three fourths its length, conical, with rounded extremity 

 connected with posterior margin by low indistinct ridge; axis segmented by 

 5— G rings, followed by a longer terminal piece. Lateral lobes depressed, feebly 

 convex, bent down slightly, with 4 — 5 indistinct low pleurse separated by faint 

 furroAvs ; first pleura the most distinct. 

 Dimensions. — 



Length of head . 8*0 mm. 



Width of ,, (over curved surface) . . 17"0 „ 



Length of glabella . . . 5*5 „ 



Width of „ at base . . . 5-0 „ 



Length of thorax .... 1O0 ,, 

 Width of axis . . . 5'0 „ 



Length of pygidium .... 4 - 5 ,, 

 Width of . . . 9-0 „ 



Remarks. — This species was compared by its authors (op. cit.) with a largo number 

 of foreign forms, but it seems unnecessary to mention species from any widely 

 different stratigraphical horizon. Proetus ramisuleatus^ Nieszk., 1 has somewhal 

 similar cranidial characters, and perhaps P. kertelensis, Schmidt, 2 is allied. Both 

 of these species occur in the highest Ordovician beds of the East Baltic provinces. 

 Collection*. — Mrs. Gray (f. M., pi. xii, figs. 9, 9 a, 10); Museum of Practical 

 Geology (f. M., pi. xii, fig. 7) ; Edinburgh Museum (f. M., pi. xii, fig. 8). 



Horizon and Localities. — Drummuck Group (U. Bala): Thraivo Glen, Drum- 

 muck Burn ; Drummuck. 



1 Nieszkowski, " Mon. Trilob. Ostseeprov.," in ' Aivhiv Naturk. Liv., Est,, Kurl.,' ser. 1, vol. i, 

 p. 560, pi. iii, figs. 1,2. 



2 Schmidt, ' Rev. Ostbalt. Silur. Trilob.,' pt. 4, p. 56, pi. iv, fig. 37. 



