MIOCENE PORPOISES — KELLOGG 121 



rather closely approximated. The interspace on the right side be- 

 tween the fifth and sixth alveolae, counting backward from the ante- 

 riormost alveola, is 8 mm., between the sixth and the seventh alveolae 

 it is 4 mm. On the right side of the rostrum the alveolae of the 20 

 posterior teeth counting forward from the hindmost one are separated 

 by rather thin septa (1 mm. or less). 



The anteriormost tooth on each side of the rostrum has the apex 

 of the crown worn off obliquely and the posterior surface of the crown 

 deeply grooved from occlusion with the corresponding tooth in the 

 mandible. Each of these large teeth is placed obliquely in the alveola 

 at the extremity of the premaxilla, and projects forward and down- 

 ward. These anteriormost teeth diverge from one another toward 

 their apices. The worn enamel crown of the anteriormost tooth on 

 the right side measures 14 mm. in length and 10 mm. in diameter at 

 the base. The ratio of the length of the enamel crown to the whole 

 tooth varies considerably in the upper tooth row, being equivalent to 

 nearly half the total length on the largest anterior teeth and about 

 one-third the total length on the larger teeth near the posterior end 

 of the tooth row. With the exception of five teeth at the anterior 

 end of the tooth row and six at the posterior end, the enamel crowns 

 of most of the remaining teeth are worn down to the roots. The 

 tooth at the posterior end of the right upper tooth row is the smallest, 

 measuring 19.7 mm. in length; the maximum diameter of the root is 

 5.8 mm. The longest anterior teeth (the fourth on left side and the 

 fifth on right side) have a length of 31 mm., and a root with a max- 

 imum diameter of 11.8 mm. The three anterior teeth on each side 

 are lodged in the premaxillae. 



The anterior mandibular teeth average smaller than the correspond- 

 ing ones in the rostrum. Behind the three anterior teeth on the right 

 side, the crowns of at least nine of the succeeding teeth were worn 

 down to the roots, although only four on the opposite side were worn 

 to the same extent. The anteriormost pair of teeth were worn 

 obliquely from occlusion with the corresponding upper teeth. On the 

 left side the second, third, fourth, and fifth teeth counting backward 

 from the first are sufiiciently complete to show that the enamel crowns 

 curved inward and backward toward their apices. The enamel crown 

 of the second tooth measures 11.5 mm. in length and 7.6 mm. in 

 breadth at the base; the total length of the tooth is 31.3 mm. Twelve 

 teeth were located in the symphyseal portions of the right and left 

 mandibles. The posterior tooth in the left mandible is the smallest 

 in this tooth row, measuring 26 mm. in length; the crown length is 

 7.5 mm., the greatest breadth of crown at base is 6.2 mm; and the 

 greatest breadth of root is 8 mm. 



