VEETBBBATE8. 195 



ORTHOPLEURODUS Novo MEXICANUS, St. J. and W. 



PL XIII, Fig. 1-3. 



Teeth below medium size, represented by forms occupying the 

 posterior position on the lower and upper jaws. 



Mandibular posterior teeth trigonal in outline, moderately arched 

 in the direction of inrollment. Antero-lateral border slightly curved 

 sigmoidally, enamel belt abrupt and well denned from the down- 

 ward and slightly outward produced basal-rim ; postero-lateral border 

 making an angle of about 55 with the opposite side ; inner margin 

 slightly obliquely produced backward from the anterior angle and 

 gently curved sigmoidally, worn specimen inbeveled inferiorly. Cor- 

 onal prominence usually well denned, rather widely expanded toward 

 the inner margin, posterior slope merging into the regularly trans- 

 versely concave posterior depression, from which the alate expansion 

 steeply rises into the prominent postero-lateral border. Surface 

 punctation exceedingly minute and widely spaced. Breadth of a 

 large specimen between the angles of the inner margin 13.5 mm. ; 

 length along antero-lateral border to point of inrollment about 

 12 mm. 



Posterior teeth of upper jaw subspatulate in outline ; antero-lateral 

 border unknown, that extremity of the teeth being extremely atten- 

 uated and in consequence mutilated ; postero-lateral border exhibit- 

 ing the characteristic straight outline, basal border slightly chan- 

 neled, and probably continued into a spur-point at the posterior angle ; 

 inner margin broadly arched backward round the coronal promi- 

 nence and thence more gently curved toward the broken anterior 

 angle. Coronal ridge prominent, rounded along the crest which 

 culminates close upon the postero-lateral border to which the sur- 

 face steeply descends, the broad anterior slope slightly depressed 

 before reaching the margin of the tooth, the ridge more or less 

 rapidly declining immediately behind the greatest prominence.. 

 Punctate structure the same as observed in the mandibular teeth. 

 An ordinary size specimen measures along the postero-lateral border 

 about 15 mm., greatest breadth of tooth at right angles to the 

 straight border 7 mm. 



The present species is determined from a few specimens of the 

 maxillary posterior form and a single example of the mandibular 

 posterior tooth, which were discovered by Mr. Springer, in the fish- 



