Measurements. A B Total length 715 [a]633 Length of rostrum 413 [a]325 Distance from occipital condyles to distal end of 612 567 maxillæ Breadth between centers of orbits 309 279 Breadth between zygomatic processes 310 278 Breadth between temporal fossæ 228 212 Breadth between postorbital processes of frontals 323 ... Breadth of rostrum at base (between maxillary 172 [b]158 notches) Breadth of rostrum at middle 40 44 Depth of rostrum at middle 52 42+ Greatest breadth of anterior nares 56 54 Greatest breadth of premaxillæ proximally 130 118 Greatest breadth of premaxillæ in front of nares 108 109 Length of temporal fossa 92 86 Depth of temporal fossa 63 46 Antero-posterior length of orbit 96 82 Breadth of foramen magnum 38 39 Length of tympanic bulla 48 ... Breadth of tympanic bulla 32 ... Length of mandible 610 ... Length of symphysis 138 ... Distance from anterior end of mandible to alveolus 166 ... [a] Tip of rostrum lacking. [b] The skull is much worn around the left notch and the measurement is only approximate. EXTERNAL FORM. The photograph of the head (Pl. 40, fig. 4) shows that the end of the beak was quite blunt, and the lower jaw quite a little longer than the upper. The superior margin of the lower jaw, which is concave in front of the tooth, is strongly convex and elevated at the side of it and behind it. The inferior margin of the upper jaw is straight anteriorly, but farther back appears to be pressed upward by the tooth. An examination of the skull shows that the mandible can be lowered so that the teeth are below the upper jaw, but when so lowered the space between the teeth and the upper jaw on each side is barely a quarter of an inch (6 mm.). With the integuments in place, it is doubtful whether the mouth could be opened any wider than is shown in the photograph. The convexity of the head, shape of the blowhole, position of the eye, etc., do not appear to differ materially from the same characters in adults of _M. bidens_. Genus ZIPHIUS Cuvier. ZIPHIUS CAVIROSTRIS Cuvier.