Reverting now to _Ziphius gervaisii_, which was mentioned on p. 30 as perhaps constituting a separate species, it will be seen by examining the figures given by Gervais[44] of the skull on which it was based that the latter presents the combination of characters peculiar to the female of _Z. cavirostris_. This skull, which was from Aresquiers (Hérault), France, was 888 mm. long, and hence, presumably, adult. The mesirostral ossification is but slightly developed, the prenarial concavity moderate, the teeth small, slender, and cylindrical, with closed roots and a diameter of 14 mm. There seems to be no sufficient reason for regarding this skull as representing a species distinct from _cavirostris_. The specimen from Buenos Ayres described and figured by Burmeister in 1868[45] was an immature male. In the skull the mesirostral ossification was lacking, the premaxillæ were flat, and the teeth conical and acuminate, with open roots, and a diameter of 12 mm. This individual was 12 feet 11½ inches (3.95 m.) long, and hence about as long as the Charleston specimen, but the skull was apparently 680 mm. long, while that of the Charleston specimen is 797 mm. long. In the latter the teeth are 45 mm. long and 10 mm. in diameter, while the tooth figured by Burmeister is 31 mm. long and 12 mm. in diameter. From these data it appears improbable that the sex of immature individuals can be determined from the skull or teeth. TEETH. The teeth of the various North Atlantic and North Pacific specimens merit a somewhat more detailed description than is given on pages 50 to 53. Six pairs of teeth from six different individuals are available for comparison. Their dimensions are as follows: _Dimensions of the teeth of Ziphius cavirostris._ Cat. Locality. Age. Sex. Teeth. No. Length. Greatest diameter. mm. mm. 21975 Charleston, South Carolina[a] Young Female 45 10 20971 Barnegat City, New Jersey Adult Female 56 13 22069 Bering Island Adult (Female?) 41 14 20993 do[b] Adult (Male?) 48 25 21248 do Adult (Male?) 58 30 49599 Newport, Rhode Island Adult Male 63 29 [a] Type of _Z. semijunctus_. [b] Type of _Z. grebnitzkii_.