VEETEBBATES. 119 



site side abruptly descending into the deep posterior depression, 

 alate lobe somewhat steeply upraised and relatively wide, trans- 

 versely convex and thickened along the border. The superficial 

 transverse rugae show strongest development in the anterior slope 

 and the posterior wing, in the latter region being nearly at right 

 angles to their course in the former space, where, in some examples, 

 at least, the surface is marked by stronger rugosities descending 

 from the crest of the median ridge. Surface punctie the same as 

 described in the opposed maxillary teeth. A specimen below medium 

 size measures across the inner margin 15 mm. ; length along antero- 

 lateral border to point of inrollment 9 mm. 



Only the posterior teeth of the upper and lower jaws of the pres- 

 ent species have been identified, represented by half a dozen 

 individuals of each form, and these, with one or two exceptions, in 

 the usual fragmentary state of preservation. Compared with the 

 forms of the species with which they are associated, C. rugosus, 

 (N. and W. sp.), the maxillary teeth are distinguishable by the rel- 

 ative greater prominence of the posterior lobe, the verrucose orna- 

 mentation of the anterior lobe, and, perhaps, the course of the 

 transverse rugae in the region of the median depression. The man- 

 dibular teeth also differ in the relative prominence, the sharply 

 rounded crest of the median lobe, depth of posterior depression, 

 proportionately greater breadth of the alate lobe, and more robust 

 build. In some of the features contrasting with the* associate species 

 there are more intimate resemblances with the Upper Burlington 

 species, C Springeri, especially as regards the mandibular posterior 

 teeth; but the maxillary teeth of the latter, again, are more like 

 those of C. rugosus, though they are not to be confounded with that 

 species. 



Geological position and localities: Keokuk limestone, main fish-bed 

 horizon; Keokuk, Bentonsport (Iowa), Hamilton, Warsaw, Nauvoo 

 and Scott county (Illinois). 



CHITONODUS LIRA.TUS, St. J. and W. 



PI. VI. Fig. 1. 



The present species is represented by a solitary imperfect exam- 

 ple of a maxillary posterior tooth, showing the anterior portion, the 

 posterior lobe having been destroyed. The part preserved, however, 

 indicates a tooth of small size, with a diameter across the inner 

 margin probably not exceeding 13 mm., with a length along the 



