May, 1919] Silurian Fossils From Ohio . 397 



From PterygometopHs intermedius, Walcott (Pal. Minnesota Geol. 

 Surv. vol. Ill, 1897, p. 728, fig. 45), from the Black River formation 

 of Illinois, Wisconsin and Minnesota, it differs chiefly in the confluence 

 of the distal parts of the first and second pairs of lateral lobes of the 

 glabella. The median parts of the glabella, between these lobes, is 

 only shghtly depressed, if at all, beneath the curvature of the latter. 

 The first pair of glabellar furrows is not convexly curved toward the 

 front. The margin of the palpebral lobes is more strongly convex 

 in outline, and their posterior margin almost reaches the posterior 

 groove of the fixed cheeks. 



With Ptervgometopus eboraceus, Clarke (Pal. Minnesota Geol. 

 Surv., Vol. Ill, 1897, p. 728, fig. 49), from the Trenton of New York, it 

 agrees in the confluence of the distal parts of the first and second pairs 

 of lateral lobes of the glabella. The cranidium of the Kentucky speci- 

 mens here described, however, is relatively much shorter. This is due 

 chiefly to the shorter length of the frontal lobe of the glabella, which is 

 less rhombic in outline, but more transversely eUiptical; the first pair of 

 glabellar furrows is more divergent, and the anterior pair of glabellar 

 lobes is less acutely triangular. The posterior margin of the palpebral 

 lobes extends nearer to the posterior groove of the fixed cheeks. Glabella 

 tuberculated ; fixed cheeks smooth. 



The specimen here figured was obtained from the Tyrone 

 member of the Black River formation, at High .Bridge, 

 Kentucky. Cranidia, agreeing in every structural detail with 

 the specimen here figured occur at the same locality. High 

 Bridge, also at two horizons in the Campnelson member of 

 the Stones River formation, 550 and 570 feet above sea level; 

 these cranidia differ from those in the Tyrone member of the 

 Black river formation only in the slightly more prominent 

 tubercles ornamenting the glabella. 



From the preceding notes it is evident that Pterygometopus 

 cofifluens belongs to a series of closely related species char- 

 acterizing the Stones River, Black River, and Trenton forma- 

 tions. Such a series is of little service for purposes of cor- 

 relation of strata in distant exposures unless the component 

 species are accurately discriminated. 



Pterygometopus achates Billings. 

 Plate XIX, Fig. 8. 



"In the specimen figured by Clarke the glabellar furrows were still 

 filled with matrix; on working them out with a needle they gave the 

 figure shown in the enclosed sketch (consisting only of the dotted part 

 of Figure 8 on Plate XIX); the second furrow slopes distinctly back- 

 ward; the third and fourth are curved, as in the photograph sent by 

 you. " (This was a photograph of Dalmanites carleyi-rogersensis, as 



