VEETEBEATES. 155 



shallow basal portion, which is somewhat expanded posteriorly; 

 inner margin broadly and regularly arched round the base of the 

 coronal prominence from the obtuse anterior angle, with a rather 

 deep concave course in the region of the posterior depression, join- 

 ing the posterior border in a subacute angle, inferiorly inbeveled. 

 Coronal ridge prominent, occupying the anterior two-thirds of the 

 area, and culminating in the broadly rounded crest a little anterior 

 of the median line; anterior slope regularly convex, the posterior 

 declivity more abruptly descending into the relatively narrow pos- 

 terior depression, which is defined by the narrow, moderately up- 

 raised, rounded alate lobe. Surface traversed by well-marked, widely 

 spaced transverse furrows, especially noticeable in the coronal prom- 

 inence, which are occupied by irregular transversely elongated pores, 

 below intervening undulations showing minute, widely spaced punctae. 

 Length of anterior articular border at least 17 mm; breadth across 

 the inner margin 20 mm. 



The unique example above described was obtained by Maj. POWELL'S 

 expedition to the Grand canon of Colorado, from the Carboniferous 

 limestone. With the exception of the outer extremity, the specimen 

 is quite entire, admitting of satisfactory comparison with allied forms. 

 Of the latter, it is, perhaps, most intimately related to Deltodus cingu- 

 latus, N. and W., of the Chester formation, being distinguished chiefly 

 by its proportionately greater breadth compared to the length of the 

 tooth, narrower and more widely spaced transverse sulci, and nar- 

 rower alate lobe. It also differs from D. Mercurii, Newb., in the 

 same respects relating to the diametral dimensions and in the dis- 

 tinct transverse undulations of the coronal region, indeed, the only 

 feature which it shows in common with that species being the nar- 

 row posterior alation. 



We have described in another place, under the specific designation 

 Deltodus propinquus, a fine large spe-cies from the Coal Measures of 

 Illinois, which, so far as relates to the homologous form, bears most 

 intimate resemblance with the present tooth. The only appreciable 

 distinctions by which the latter teeth may be distinguished consist 

 in the greater obliquity of the inner margin and the undulations 

 traversing the crown, indeed, worn examples, in which the longitu- 

 dinal undulations are obsolete, are hardly recognizable from the tooth 

 above described. 



The specific designation is given in honor of Major J. W. POWELL, 

 U, 8. Geologist, in charge of the geographical and geological explor- 

 ation of the Eocky Mountain region. The unique type is deposited 



