RAYMOND: SOME nkw ORDOVICIAN TRIL0BITE8. 283 



HoLOicETOPUS Angeltn. Glabella Btrongly outlined. Byes about their 

 own length from the posterior margiD. 



Type, Holovu topua litnbatus Angelin. 



Lower Ordovician, Scandinavia and eastern North America. 



Brontkopsis ckkgaria, sp. nov. 



Holometopw (myelin) Hillings (partini), Palaeozoic foss. Canada, 1865, 1, p. 

 281. Non, p. 95, fig. 85. 



Cranidium much expanded at the front, so that it is wider than long. Gla- 

 bella convex, prominent, expanded at the anterior end, the width there being 

 equal to about three fourths the length. The glabella tapers rapidly toward 

 the narrowest place, at the neck-ring, and has an obscure median carina on its 

 posterior half. In the dorsal furrows are obscure indications of three pairs 

 of pits, one pair close to the anterior margin and two pairs on the constricted 

 "neck" of the glabella, these being obscure glabellar furrows. The fixed 

 cheeks form wide flattened bands on either side of the glabella and opposite 

 its narrow part, are raised nearly or quite as high as the glabella itself. The 

 neck-ring bears a small median tubercle. 



Pygidium approximately semicircular in outline, convex, with a narrow 

 concave border. Axial lobe long, the acutely tapering posterior end continu- 

 ing though only faintly raised, to the border. At the anterior end of the axial 

 lobe are three well-defined rings, behind which there are two or three rather 

 obscure ones. The pleural lobes are smooth, except for an anterior rib. The 

 smaller specimens are nearly flat, and the posterior portion of the axial lobe 

 more clearly defined than in the large ones. 



Measurements: — Length cranidium, 7.5 mm., width at front, 9 mm. 

 Width glabella at front, 5.5 mm., at neck furrow, 3.5 mm. Length pygidium 

 4 mm., width, 7.5 mm. 



Horizon and Locality : — The types are from the base of the 

 Liberty Hall limestone at Lexington, Va., where the species is common. 

 It is also common at the top of the Holston at the Thomas farm, three 

 miles northeast of Blacksburg, Va., and in the Athens at Chatham 

 Hill, on the northern slope of Walker Mountain, north of Marion, Va. 

 A single specimen was found above the middle of the Holston on the 

 Hoge farm seven miles south of Bland, Bland Co., Va., and another 

 single specimen in the middle Ottosee, seven miles north of Mendota. 

 Specimens from these three localities are in entire agreement. In 

 Tennessee I found it at only one locality, between the Holston and 

 Tellico, in South Knoxville. 



