FOSSILS OF THE CLINTON GROUP. 119 



ularly disposed, varying but little in their distance from each other, and 

 counting about eighteen in one-half of the circumference of the shell, the 

 spaces between the ridges deeply concave, and sometimes showing evi- 

 dence of finer intermediate strise. The transverse ridges are as strongly 

 elevated as the longitudinal ones, but less angular on the crest, more dis- 

 tantly and irregularly disposed, the intervening spaces being sometimes 

 two or three times as great as the narrowest spaces observed on the frag- 

 ment, the spaces between them finely striated, the striae undulating be- 

 tween the longitudinal ridges. 



The species appears to be of the same type with 0. columnare, Hall, 

 but diflers from any species of that group yet described, in the strong, 

 irregularly arranged, transverse ridges, and the greater number of longi- 

 tudinal ridges. The species of that group known have the fine trans- 

 verse strise crossing the longitudinal flutings, but we believe there are 

 none known having the transverse ridges. 



Formation and locality : In the iron ore beds of the Clinton group, Clinton county, 

 Ohio. Collection of IT. P. James, Esq. 



CRUSTACEA. 



G-ENUS ILL^NUS, Dalman. 

 Ill^nus Daytonensis (n. sp.). 



Plate 5, fig. 14-16. 



Among the fossils obtained from the quarries at the Soldiers' Home, 

 near Dayton, detached specimens of the glabellse and pygidia of a species 

 of lUsenus are not uncommon. The glabella is wider than long, and 

 quite regularly rounded in front, between the junction of the suture lines 

 with the anterior margin of the head, the surface being highly convex, 

 with a slight tendency to gibbosity in the middle, when viewed side- 

 ways. The 'dorsal furrows on the cast are broad and strongly marked, 

 extending about one-third of the length of the head from the posterior 

 margin, and terminating anteriorly in a rather large oval depression, 

 the space between them more abruptly convex than in front. Posterior 

 margin between the furrows more strongly rounded than the front of the 

 head, the whole occipital border being deeply trilobed, from the depressions 

 of the dorsal furrows in the margin. Fixed cheeks a little more than 

 half as wide as the space between the dorsal furrows, strongly convex 

 opposite and posterior to the eyes, not distinguishable from the other por- 



