RAYMOND: SOME M w OBDOVICIAM TRILOBITES. 275 



ating branching ridges and small shallow pits. The t\\<> principal "nervures" 

 originate on cither side of the glabella just in front <>f the lateral furrows and 

 nm diagonally backward, reaching the neck furrow some distance inside the 

 genal angles. Those on the right check of one specimen uol only branch, 

 l)u t in t he outer part of their <•< urse, t he two unite, showing conclusively thai 

 they are not facial sutures. The cephalon has a narrow, upturned rim around 

 its border, and in the concentric depression within this is m row of pits which 

 are larger and deeper than the others on die cepbalon. The aeck-furrow 



is linear, clearly impressed and the neck-segment smooth. As usual in the 



genus, the facial suture is marginal except at the genal angles, where it cuts 

 off the spines. These latter are not sat isfactorily preserved on any specimens 

 but apparently were not Long enough to reach beyond the third thoracic seg- 

 ment, a very unusual feature in this genus, and Leading one to suspect that the 

 specimens are incomplete in this regard. 



Thorax with six narrow segments, the fust of which is a little wider than the 

 BUCCeeding ones, but not differently marked. Axial lobe narrow, each ring 

 show ing the diagonal furrow at the sides as is usual in the genus. The furrows 

 on the pleural lobes divide each Lateral portion of a segment into an anterior 

 area which is pitted like the fixed cheeks, and a narrower smooth posterior 

 part. 



The pygidium is about twice as wide as long, rounded in outline, with, in 

 some cases, sufficient straightness of sides to produce a slight triangularity. 

 Axial lobe narrow, with about fifteen rings, and pleural lobes with about 

 twelve pairs of furrowed ribs which extend to the edge. Surface pitted, 

 like that of fixed cheeks. 



Measurements: — One specimen is 15.5 mm. long, 13 mm. wide at the 

 genal angles. The pygidium is 5.5 mm. long, 11.5 mm. wide, thorax 4.5 mm. 

 long, cepbalon, 5.5 mm. long. Another specimen is 15 mm. long, and 12.5 mm. 

 wide. A third specimen is 19.5 mm. long, and 15 mm. wide. 



A cephalon is 6 mm. long and 18 mm. wide; distance from back to front 

 of glabella, 4 mm., width of glabella 4.5 mm. 



This species is more like Dionidc richardsoni Reed than any other 

 known species of the genus. The likeness is emphasized particularly 

 by the ornamentation of the thorax. It has, however, fewer rings 

 and ribs on the pygidium, a wider cephalon and narrower axial lobe. 

 The ornamentation of the thorax and pygidium separates it from all 

 other species. 



Horizon and Locality : — This species has so far been found only 

 at a locality about 100 feet below the top of the Athens shale about 

 three miles northeast of Blacksburg, Va., where it was collected by 

 Professor Holden, for whom it is named. The associated fossils are 

 typical Xormanskill graptolites, brachiopods, and trilobites. Holo- 

 type M. ('. Z. 1,590. 



