282 bulletin: museum 01 comparative eo5loot. 



at the front, tapering regularly backward. There are four well-marked ri 

 Pleural lobes practically Sat, apparently crossed by obscure ribs, bul all 

 specimens are exfoliated, showing a wide striated doublure. The posterior 

 margin shows two pairs of short flat spines, the inner ones being wider than 

 the outer, and extending practically as far back. 

 Measi rjbments: — A large cranidium is 15.5 nun. long, and 15 mm. wide 



at the palpebral lobes. Nine segments of a thorax are 7..") mm. Long, 1 mm. 

 wide at the anterior end and 3.5 mm. wide at the posterior. The axial lobe 

 i- 2.5 mm. wide at the front. A pygidium is 10 mm. long, 10 mm. wide it 

 the anterior end and mm. wide at the posterior end. The axial lobe i> ."> mm. 

 wide at the anterior end and 7.5 mm. Long. 



This species is exceedingly abundant in the Athens at Saltville, 

 Va., and though no complete specimens have so far been found, it is 

 now known from all the parts, including the hypostome, which can- 

 not be said of any other species of the genus. It differs hut little 

 from Robergia schlotheimi, such differences as there are being in the 

 pygidium, which has a longer and wider axial lobe, is more nearly 

 square, and has a straighter posterior margin. It differs from the 

 Swedish R. microptkalma chiefly in the pygidium which is much more 

 nearly square and has two instead of three pairs of spines. 



Horizon and Locality: — A very abundant species in the lower 

 part of the Athens at Saltville, Va., but not yet found elsewhere. 

 Cotypes M. C. X. 1,601 to 1,606. 



Styginidae, fain, now 



Approximately isopygous Opisthoparia with glabella greatly expanded 

 at the front, anterior portions of the facial sutures widely divergent, eyes 

 typically very far back. Thorax of nine segments in the typical genus. Pygid- 

 ium with well-defined, long axial lobe, pleural lobes smooth or with faint 

 furrows. 



Stygina Salter. Glabella only faintly outlined, without furrows. Eyes 

 close to posterior margin. 



Type, Stygina latifrons (Portlock). 

 Ordovician, Scandinavia, and British Isles. 



Bronteopsis Nicholson and Etheridge. Glabella strongly outlined, with 

 or without three pain of furrows. Eyes close to posterior margin. 



Type, Bronteopsis scotia Nicholson and Etheridge. 



Ordovician, Sweden, Great Britain, and eastern North America. 



