true: the type of anoplonassa forcipata 101 



alveoli to those of Anoplonassa is very striking and is, I think, the result 

 of a similar mode of dental growth. 



The fragment from the anterior end of the symphysis of the mandible 

 which constitutes the type of Anoplonassa, is nearly straight in its pos- 

 terior two-thirds, hut the tip is quite sharply curved upward, and, as al- 

 ready stated, considerably expanded. Just behind this expanded portion, 

 the jaw is slightly constricted. These characters are, strictly speaking, 

 peculiar to Anoplonassa as compared with recent ziphioids, but in adult 

 or old specimens of Ziphius the superior surface of the symphysial region 

 is curved upward, as in Bei'ardius, although this surface is plane, the 

 end of the jaw is rounded, and the terminal alveoli are directed upward 

 rather than forward. 



In cross-section, the type of Anoplonassa is shield-shaped, or rather, 

 triangular, with one plane side (superior) and two convex sides. The 

 chord of the convex sides of the jaw does not exceed the breadth of 

 the superior surface, or in other words, a cross-section of the jaw 

 has nearly the form of an equilateral triangle. On casual examination, 

 it would appear that in Anoplonassa the symphysis is not as deep in pro- 

 portion to its breadth as in existing ziphioids, but a comparison of 

 measurements shows that in Mesoplodon and Berardius the breadth of 

 the extremity of the jaw is about as great as its depth, and in adult 

 Ziphius -the breadth is considerably greater than the depth. It thus 

 becomes obvious that it is not the breadth of the symphysis that makes 

 the jaw of Anoplonassa seem so slender, but its great length. The ap- 

 pearance of the specimen indicates that only a portion of the symphysis 

 has been preserved, and that the whole symphysis was much longer. 

 Even in the fragment, however, the length is 6 times the depth, while in 

 Ziphius and Mesoplodon the length of the complete symphysis is only 

 from 2£ to 5^- times its greatest depth, and in Berardius but 2 times its 

 depth. 



It is difficult to conjecture how long the complete symphysis of 

 Anoplonassa was originally, or what was the length of the entire man- 

 dible. That the symphysis was much longer than the fragment pre- 

 served is, as already stated, extremely probable, since the width at the 

 posterior end of the fragment is only 7 mm. greater than the width 

 immediately behind the posterior pair of alveoli. It is certain that the 

 general conformation of the mandible must have been very different 

 from that of any existing ziphioid, and that it resembled rather the 

 mandible of a sperm whale (Physeter), or of one of the Plantanistidae, 

 such as Platanista or Stenodelphis. If the upper jaw was equally 



