656 PROCEEDINGS OF THE NATIONAL MU8EUM. vol. 45. 



concealed by the integuments and their position could not be definitely 

 determined until the latter were removed. The distance from the 

 alveolus of each tooth to the apex of the jaw, obliquely, is 12 mm.; 

 from the alveolus to the median line, 7 mm. As already mentioned, 

 the teeth are inclined forward at an angle of 45° and also slightly out- 

 v/ard. They project 4 mm. above the upper margin of the jaw. 



The teeth are fusiform and slightly curved, and compressed. Their 

 length is about 30 mm. and their greatest diameter about 9 mm. The 

 tips are very acute and appear to be devoid of enamel.^ 



j Dimensions of the type-skull of Mesoplodon jnirum, Cat. No. 175019, U.S.N.M. 



mm. 



Total length •. 810 



Length of rostnim 496 



Length from tip of rostrum to posterior end of pterygoids in median line 618 



Greatest height from vertex to inferior border of pterygoids 301 



Breadth across centers of orbits 325 



Breadth between zygomatic processes 345 



Breadth between bases of anteorbital notches 210 



Breadth at middle of beak 60 



Breadth across occipital condyles 125 



Breadth of expanded proximal ends of premaxillse behind anterior nares 142 



Least breadth of premaxillae opposite anterior nares 118 



Breadth of premaxillae opposite preraaxillary foramina 68 



Greatest breadth of anterior nares 56 



Least distance between maxillary foramina 92 



Distance from posterior border of maxillary foramen to end of maxillary pro- 

 tuberance 63 



Length of portion of vomer visible on palate 162 



Len"gth of mandible 668 



Length of symphysis 193 



Greatest height of mandible opposite coronoid process 117 



The skull of Mesoplodon mirum presents a close general resemblance 

 to that of M. europxus, except in the position of the teeth. The 

 species belongs to that section of the genus which is characterized 

 by the absence of the basirostral groove, and comprises the species 

 mirum, hidens, europseus, liectori, and stejnegeri. From hidens the 

 present species differs in possessing a shorter and broader rostrum, 

 more closely approximated premaxillae, more prominent maxillary 

 ridges and deeper anteorbital notch, broader maxillary frontal plates, 

 a smaller anterior projection of the palatines, larger temporal fossae, 

 differently shaped lachrymal and pterygoid bones, and many other 

 characters. 



From europseus it differs in the form of the rostrum, lachrymal and 

 pterygoid bones, and other characters as indicated in the foregoing 

 description. 



1 The teeth have been fixed in their natural position in the jaw, an(J it seeipa undesirable to extract tbero. 

 On that account it is not possible to give esact dimensionSv 



