VEETEBRATB8. 131 



GENUS PCBCILODUS, Agassiz. 

 PCECILODUS VAKSOVIENSIS, St. J. and W. 



PI. VIII, Fig. 13, 14. 



Posterior teeth of the upper jaw of small size, subelliptical in 

 outline, strongly arched in the direction of inrollment. Antero- 

 lateral border slightly oblique to the inner margin forward and out- 

 ward; postero lateral border gently arched and converging toward 

 inrolled outer margin at an angle of 30, more or less, with the 

 antero-lateral border; inner margin moderately concave in the 

 median region, broadly arched round the posterior lobe to the 

 acutely rounded extremity, and similarly arched round the base of 

 the less' prominent anterior lobe to the obtuse anterior angle. Cor- 

 onal region presenting a very oblique, moderately elevated, regularly 

 transversely arched posterior lobe, a slight sulcus extending along 

 the outer side parallel with the postero-lateral border, anteriorly 

 defined by the moderately excavated median depression; the muti- 

 lated condition of the neck does not permit the contour of the 

 anterior lobe to be satisfactorily made out, although it seems to 

 have been moderately arched transversely. The posterior lobe shows 

 a few relatively strong transverse corrugations, which are obsolete 

 in worn examples ; surface punctation fine and moderately spaced' 

 Transverse diameter of a mature tooth at the inner margin 12.5 mm. ; 

 length of autero-lateral border 4 mm. 



The above species is represented, in the collection of Mr. Van 

 Home by only two examples of the maxillary terminal form. The 

 specimens are mutilated in the anterior region, but the posterior 

 prominence exhibits the characteristic contour prevalent in certain 

 species of the genus, hence its present reference. The transverse 

 undulations of the posterior lobe recall the Chester species, P. Ces- 

 tnensis, although they are less in number and not so deeply im- 

 pressed in the interspaces; while the antero-lateral border seems 

 to be longer and less obliquely curved outward and forward. Its 

 relations with P. St. Ludovicl are much less intimate, the presence 

 of the transverse corrugations of the posterior lobe offering a marked 

 distinguishing feature in contrast with that species. Should the 

 anterior lobe be found, from the examination of perfect individuals 

 to present a regularly convex elevation, instead of an angularly 

 arched ridge, such as is characteristic of the genus Poncilodus, the 



