522 GEOLOGY OF OHIO. 



A Description of the Trilobites, Mouajsks and Brachiopod? 

 of the Clinton Grouv of Ohio and Indiana. 



Acidaspis Ortoni. Foerste. 



(Plate 25, Fig. 23 ; Plate 27, Fig. 1.) 



This species was first described from the Clinton rock at Brown's 

 quarry where the species, although by no means common, at least occurs 

 in every day's collecting (Bulletin of Denison University Lab. volumes 

 I and II). In the "Orthoceras block" from the base of the Clinton at 

 Huffman's quarry several heads were found. In the siliceous Clinton, 

 near Lockport, New York, the same form seems to occur, judging by 

 specimens in the cabinet of Dr. E. N. S. Ringueberg. 



Very little has been added to our knowledge of this species by recent 

 investigations. The occipital segment is prolonged and pointed posteri- 

 orly, In a specimen from the "Orthoceras block," the head anterior to 

 the occipital groove was 5 mm. long; the occipital segment was 3.3 mm. 

 broad, and 3 mm. long, the postero-lateral sides of the segment having 

 a concave outline owing to the posterior prolongation. In the more ma- 

 ture specimens the proportions are not maintained, but the prolongation 

 of the occipital segment posteriorly is always discernable. The "Ortho- 

 ceras block" specimens showed longer spines along the margin of the 

 free cheek than any hitherto observed. The longest spines are fully 2.7 

 mm. long. The ridge running from the eye anteriorly curves around 

 inwardly so as to connect with the anterior margin of the glabella, being 

 depressed, however, just before reaching the more convex outline of the 

 margin. A groove outlines the anterior of ihe glabella and passes thence 

 along the border of the free cheek. Anterior to this groove in that por- 

 tion of the head anterior to the glabella the marginal border follows a 

 slightly more convex outline than it does along the free cheeks, thus this 

 portion of the border is advanced slightly beyond the general outline of 

 the head, but whether this median portion of the border possessed spines 

 or not is unknown. It is, of course, impossible to determine whether 

 this species is distinct from the A. fimbriate/,, Hall, until that species is 

 better known, but the figure of the free cheek of that species, published, 

 indicates a bend in the postero-lateral spine which is not present in any 

 Ohio specimens. 



Acidaspis brevisfiinosa, sp uov. 



(Plate 37A. Fig. 18.) 



At Huffman's quarry is found a free cheek which may be easily dis- 

 tinguished from that of A. Ortoni by the shortness of the lateral spines, 

 these being scarcely more than lateral monticules in the anterior and poster- 

 ior parts of the series. The spines,' moreover, are not perpendicular to the 

 outline of the free cheek but where longest are directed postero-laterally. 

 Finally the spines do not cease opposite the general posterior outline of 

 the head but are found some distance down the side of the great postero- 

 lateral spine, in which the free check terminates. 



