BEAKED WHALES, FAMILY ZIPHIID^ TRUE. 9 



MESOPLODON DENSIROSTRIS (Blainville) ? 



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

 Ziphhis seychellensis Gray, Zool. Erebus and Terror, 1846, p. 28. 



The skull of the specimen from Aimisquam, 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, especialty those of the beak, are warped by weathering. The proximal 

 extremit}' of the left premaxilla is lacking and also the tip of the beak. 



The skull is obviously that of a J'oimg 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 skidl, with a few exceptions, agree well with 

 those of 3'oung specimens of 31. 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 premaxilhie 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 premaxillfe are higher than the maxillae on which they rest. 

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

 species of Mesoplodon, 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 j^ortion 

 of the premaxillge is that of M. densirostns. 



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 hidens, ends at a point about 90 mm. in front 

 of the line 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 hidens. 



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 maxillse are much broader 

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

 of the notch. The premaxilla? are noticeably constricted immediate^ 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 premaxillse is nearly vertical. The anterior nares are noticeablj' 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 pterj^goids 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 



