FOSSILS OF THE CLINTON GROUP. 525 



glabellum, 3.5; of the sub-marginal groove, 5 mm., an advance towards C 

 Christyi with glabella only half the length of the head. 



Illcsnus Daytonensis, Hall and Whitfield. 



(Plate 26, Figs. 4rz, b ; Fig-. 6; Figs, la, b, c ; Plate 27, Figs. 6, 10a.! 



This species is found in the limestones at Soldiers' Home, Centerville, 

 Brown's quarry, Yellow Springs, Ludlow Falls, Fair Haven, Todd's Fork 

 Fauver's quarry, in the "Orthoceras block " at Huffman's quarry, and at 

 Hanover, Indiana. It occurs also in the flinty Clinton at L-ockport, N. Y., in 

 the collection of Dr. E. N. S. Ringueberg. In the quarry in John Glaser's 

 woods, on Brandt pike, a glabella. 



Iltcenus ambiguus, Foerste. 



(Plate 2fi, Figs 9 a, b; Figs. 10 a, b, c; Fig. 11?) 



Typical specimens occur in the limestone at the Soldiers' Home 

 quarries, Fauver's quarry, the quarry in John Glaser's wood on Brandt 

 pike, 5^- miles northeast of Dayton, Fair Haven, Todd's Fork and Han- 

 over, Indiana, in the limestones. Somewhat similar specimens occur in 

 the Niagara shales at Lockport, N. Y., but it will require further study 

 to discriminate them from /. loxus, Hall. 



In its typical development the pygidium presents an almost semi-circu- 

 lar outline, and a surface which is moderately convex above, but which 

 increases in curvature greatly towards the posterior and lateral borders. Not 

 the slightest trace of a marginal concave curvature ought to be seen towards 

 theborder. This pygidium differs from that of ///. insig?iis solely in its con- 

 stantly much smaller size, and in its semi-circular outline, there being no 

 trace of elongation as in the latter species. The Niagara specimen from 

 Springfield, Ohio, figured in the Pal. of Ohio, vol. I, plate 15, fig. 5, is of 

 the type of ///. ambiguus. III. insignis, has a somewhat elongated pygi- 

 dium, as described later. 



Idcenus insignis, Hall. 



(Plate 26, Fig. 11?} 



Pygidia having the characteristics of this species are found in the 

 limestone at Soldiers' Home. The corresponding heads show stronger 

 dorsal furrows than is indicated in published figures of this species. 

 They are stronger on the lower cast than on the upper surface of the orig- 

 inal. The specimens usually attain large size, equalling those from 

 Wisconsin. The pygidium, though rounded along the entire exterior mar- 

 gin, is distinctly though not strongly elongated. It attains its greatest 

 height and also its greatest convexity towards the posterior two-fifths of 



