VEBTEBBATES. 107 



Posterior tooth of the lower jaw known only from very imperfectly 

 preserved examples, which, however, shows a rather prominent and 

 regularly arched median lobe, situate nearly centrally, with appar- 

 ently well-developed posterior wing, nearly equalling in breadth the 

 plane anterior area. 



The above described species is represented in the collections by 

 only a few examples, and in only two exceptions are the complete 

 outline and coronal contour shown. From these we are led to 

 recognize distinctive peculiarities that readily distinguish the teeth 

 from congeneric forms previously noticed, with the exception in 

 favor of the possible identity of the Keokuk forms with the present 

 species. 



Geological position and locality : Warsaw limestone ; Golden Bluffs, 

 near Warsaw, Illinois. 



STENOPTERODUS PARVULUS, (N. and W. sp.) 



PL IV, Fig. 4-8. 



Sandalodus parvulus (in part), Newberry and Worthen, 1866, 111. Gaol. Surv., II, p. 102, 



PI. X, f.l. 



The recognition of the above cited species was based upon a 

 unique, nearly perfect tooth, representing the posterior form per- 

 taining to the upper jaw. The specimen is mutilated along the 

 outer margin in front, the inrolled extremity being broken away. 

 The figure, however, conveys a very inadequate impression of the 

 coronal contour, the engraving exaggerating the accidental features 

 traceable to attrition at the expense of the natural contour surfaces. 

 The specimen exhibits the posterior lobe of the crown, gradually 

 culminating anteriorly, where it is suddenly broken down and denned 

 by a slight depression from the plane anterior area with which it 

 merges in the middle outer region of the coronal surface, where the 

 tooth has been subjected to excessive attrition while in use. In the 

 outward and forward obliquity of the antero-lateral border, also in the 

 distinct definition of the shallow enamel fold along the still more 

 oblique and gently arched postero-lateral border, where the basal 

 portion forms a prominent rim, reaching to the point of inrollment, 

 the original figure above cited conveys a more accurate idea of the 

 form. 



The acquisitions of Mr. Van Home include a beautiful series of 

 the above mentioned teeth, with which are associated, equally nu- 

 merous, another form, which we have come to regard with a strong 



