240 NORTH AMERICAN INDEX FOSSILS. 



17. 0. minor Nicholson. (Fig. 1525, c.) Ordovicic. 

 Annulations sometimes faintly marked on side opposite to the 



attached side, about fifteen in ^q inch; curvature simple or 

 S-shaped; length %o to %q inch; diameter at mouth %o to %5 

 inch. 



Cincinnati group of Ohio, common. 



18. 0. intemedia Nicholson. (Fig. 1525,0, &.) Devonic. 

 Straight or flexuous, sometimes bent at nearly right angles in 



the lower part (Cornulites hamilt nice 'Gr3ib2iu) ; larger than pre- 

 ceding, more robust and with more distant annulations, which may 

 be extended in wing-like prolongations for attachment. 



On corals, brachiopods, etc., Hamilton shales, Thedford, On- 

 tario, and western New York. 



Suborder Errantia. 

 Annelid Jaws and Conodonts. 

 These microscopic teeth are of uncertain systematic position, 

 especially the conodonts which were at first considered to be fish 

 teeth, and have been regarded as pertaining to the lingual ribbon of 

 molluscs, or to Crustacea ; they are translucent, of a shining, reddish 

 horn color, and are composed of carbonate and phosphate of lime; 

 they exhibit a great variety of form; the jaws and toothed plates 

 have the character of the jaws of modern annelids. Some of the 

 more important American types are here given: 



A. Jaws. 

 VI. Arabellites Hinde. 

 Jaws of three kinds: (i) an extremely prominent anterior hook 

 and a row of smaller teeth on a wide base; (2) sickle-shaped, and 



^^ K^^^ ^^£^ 



Fig, 1526. Annelid jaws from the Lorraine : a, Ginonites serratus , yc^% \ b, (E. 

 rostratus, X ^o 5 <^» ^- ciineatus^ X 1° + 5 ^^» Arabellites hamatus, X ^A- (After 

 Hinde. ) 



(3) quadrate jaws with straight upper edge of small teeth. 

 Ordovicic-Devonic. 



Examples: 19, A. hamatus Hinde Lorraine (Fig. 1526, d) ; 20, 



