100 bulletin: museum of comparative zoology. 



The opposite walls approach each other more frequently, and in a few- 

 places are bridged by transverse septa almost on the level of the superior 

 surface. The groove has in consequence somewhat the appearance of a 

 succession of shallow, elongated alveoli. Except at one point, however 

 it is improbable that any teeth were implanted in the jaw posterior to 

 the large terminal pair, though some small rudimentary teeth may have 

 been, and probably were, imbedded in the integuments above the groove, 

 as in many specimens of recent ziphioids. At the point on the alveolar 

 groove of Anoplonassa already referred to, at a distance of about 47 mm. 

 posterior to the large terminal alveolus, is a second smaller and shallower 

 one of an elliptical form. On the left side this has a length of about 13 

 mm., a width of about 7 mm., and a depth of about 3 mm. The floor 

 has a granular appearance similar to that of the anterior alveolus. There 

 can be no doubt that a pair of teeth was originally implanted in the jaw 

 at this point, similar to, but much smaller than, the anterior pair, Ano- 

 plonassa in this respect resembling Berardius. 



The large anterior pair of alveoli is situated immediately at the tip of 

 the mandible. They occupy the whole width of the extremity of the jaw, 

 which is considerably expanded to receive them. They are separated 

 by a common median wall only about 4 mm. in breadth. Each alveolus 

 is about 23 mm. long, 16 mm. broad, and has a maximum depth of about 

 5 mm. In the centre of each depression is a papilliform elevation. The 

 whole floor of the alveolus is granular in appearance, as already men- 

 tioned, and consists of a. fine bony network, surrounding small vascular 

 openings. In these alveoli a pair of large teeth undoubtedly rested, as in 

 Ziphius or Berardius. It is well known that in young ziphioids, and 

 especially in the two genera just mentioned, the teeth are implanted in 

 very deep alveoli, with only the tip projecting above the superior surface 

 of the mandible. As the teeth grow they are pushed out more and more, 

 so that finally their roots are scarcely at all below the superior surface of 

 the jaw. In the meantime the vascular pulp below them ossifies and fills 

 the alveolar cavity almost to the top, and on the upper surface of this 

 bony network rests the root of the mature tooth. 



This last stage is shown in the mandible of an adult Ziphius (Cat. No. 

 49599), from Newport, R.I., in the U. S. National Museum. Here the 

 large anterior alveoli are filled to within about 12 mm. of the free 

 margins with a spongy mass of bone, the upper surface of which is 

 somewhat depressed. 



The anterior alveoli of an adult Berardius bairdii from Bering Id. 

 present a similar appearance on a larger scale. The resemblance of these 



