396. The Ohio Journal of Science [Vol. XIX, No. 7, 



with the adjacent part of the pygidium. The pleiiral ribs end abruptly 

 along the line of deflection, the broadly rounded ends of the ribs project- 

 ing slightly beyond this line, the marginal part beneath being smooth. 

 In the figured pygidium of Platycoryphe dubius, the marginal part of 

 the pygidium, beneath the line of deflection, was not exposed, and hence 

 the line of deflection was regarded, in the original description, as the 

 lateral margin of the pygidium. However, the broadly rounded 

 terminations of the pleural ribs, along this line of deflection, are distinctly 

 visible. Compared with the pygidium of Platycoryphe dubius, the 

 axial lobe of Platycoryphe platycephalus is more convex, and the furrows 

 separating the pleural ribs are distinct as far as the line of deflection 

 of the lateral margin. 



Platycoryphe dubius is characteristic of the Girardeau limestone, in 

 Alexander county, Illinois. Cranidia of Platycoryphe occur also in the 

 Maquoketa, near Yorkville, Illinois. These resemble the cranidia of 

 Platycoryphe christyi, from the Waynesville member of the Richmond 

 of Ohio; if distinguishing features occur, the later have not been noticed. 

 The pits in the anterior part of the dorsal furrows are small and nearly 

 obsolete. 



Ceraurinus cf. trentonensis Barton. 

 Plate XIX, Fig. 7. 



Imperfect cranidium. Glabella relatively broader than in Cer- 

 aurinus trentonensis Barton, from the Trenton on Goat Island, in the 

 northern part of Lake Huron; the lateral outlines of the lateral lobes 

 are less curved; the third pair of glabellar furrows is more oblique, 

 reaching the occipital groove at points less than the width of the third 

 pair of glabellar lobes apart. From the Kimmswick (Prosser) lime- 

 stone on Sanders Branch, in Ralls county, Missouri. 



Pterygometopus confluens, sp. nov. 

 Plate XIX, Fig. 19. 



This species differs from Pterygometopus caUiccphalus, Hall, 

 (Pal. Minnesota Geol. Surv., Vol. Ill, 1S97, p. 731, fig. 51), from 

 the Trenton of New York, chiefly in the confluence of the distal parts 

 of the first and second pairs of lateral lobes of the glabella; the postero- 

 lateral angles of the second pair is rounded. The posterior pair of 

 lobes is small, circular, distinctly defined from the median parts of 

 the glabella, and is located directly beneath the rounded postero-lateral 

 angle of the second pair of lobes. The second pair of lobes also is dis- 

 tinctly defined from the median part of the glabella, and a similar 

 tendency, though much less marked, is shown also by the first pair 

 of lobes^ The posterior pair of lobes indents slightly the lateral parts 

 of the neck segment. Between the posterior lobes, the median part 

 of the glabella is transversely rather strongly convex, but between 

 the first and second pairs of lobes the convexity of the median part 

 of the glabella is moderate, and this part of the glabella is at about the 

 same level as the adjacent lateral lobes or is only slightly below the 

 curvature of the latter. 



