BEAKED WHALES, FAMILY ZIPHIIDa: TRUE. 9 



MESOPLODON DENSIROSTRIS (Blainvillej ? 



Delphinus deimrostris Blainville, Nouv. Diet. Hist. Nat., 2d ed., vol. 9, 1817, p. 178. 

 Ziphius seychelUnsis Gray, Zool. Erebus and Terror, 1846, p. 28. 



The skull of the specimen from Annisquam, Mass., (PI. 1, fig. 2) is, I regret 

 to saj', in rather poor condition. It is broken in the left orbital region, and all 

 the bones, especially those of the beak, are warped by weathering. The proximal 

 extremity of the left premaxilla is lacking and also the tip of the beak. 



The skull is obviously that of a young animal, as all the sutures are open and 

 the surface of the occipital condyles is pitted, owing to imperfect ossification. 



Although the dimensions of the skull, with a few exceptions, agree well with 

 those of young specimens of M. hidens, as shown by the foregoing table (p. 8), 

 certain differences stand out conspicuously. The most salient of these is the depth 

 of the beak as a whole and the depth and shape of the rostral portion of the pre- 

 maxilla?. The latter portion of the premaxillae instead of being low, with a straight 

 inferior margin, is very high, with the inferior margin strongly convex. At the 

 middle of the beak the premaxilhe are higher than the maxilla? on which they rest. 

 It is true that the shape of the beak varies greatly with age in bidens and other 

 species of Mesojdodon, but I do not find any evidence that such a change as is here 

 indicated takes place in hidens. The form of the beak and of the rostral portion 

 of the premaxUlae is that of M. densirostris. 



The beak is almost as broad at the base as in hidens, but the lateral free margin 

 of the maxilla anterior to the anteorbital notch instead of continuing along the side 

 of the beak nearly to the tip, as in bidens, ends at a point about 90 mm. in front 

 of the fine of the notch, beyond which the sides of the beak are vertical. 



The margin of the maxilla immediately anterior to the anteorbital notch is a 

 little damaged, but there was apparently no strong tubercle at this point, and the 

 surface of the maxilla, though convex, is not raised into a distinct ridge. In a 

 young skull, however, one would not expect to find a high ridge. The palatines 

 are visible from above, which is not the case in bidens. 



The maxillary foramen is situated a little in advance of the premaxillary 

 foramen and is directed forward, and, as Dr. Glover M. Allen has pointed out, 

 connects with a broad groove which runs forward along the triangular, horizontal 

 portion of the maxilla at the base of the beak. The maxillas are much broader 

 behind the notch than in bidens, and the anterior end of the malar forms the bottom 

 of the notch. The premaxilla? are noticeably constricted immediately in front of 

 the premaxillary foramina, and the expanded portion just behind these foramina 

 is nearly horizontal, with a low transverse ridge near the middle. The proximal 

 end of the premaxilla? is nearly vertical. The anterior nares are noticeably small. 

 The foramen magnum is large, with a trifoliate outline (PI. 10, fig. 2). The palate 

 at the proximal end presents a median ridge with a narrow groove on each side. 

 The palatines extend as a broad band much beyond the pterygoids anteriorly. 

 The vomer is visible below for a space of 142 mm. near the end of the beak. A 

 very small piece is also visible at the base of the beak, between the palatines and 



