able to give a figure (plate XVII.) from a photograph which I had taken by permission of Prof. Hutton. The other group, of which the type of M. hectori is an extreme though very young example, represents the forms similar to M. europœus of the northern seas.

These extreme forms are separated, but with many intermediate examples, chiefly on account of the position and size of the tooth in the mandible, a character to which I think too much importance has been attached, as no two specimens yet obtained agree perfectly in this respect.

The complete skeleton of an adult male of M. hectori which I obtained in Lyall Bay, near Wellington, in January, 1875,^* agreed perfectly with those parts which had been preserved by the late Dr. Knox of the type of the species from Tetai Bay, Porirua Harbour, but in this second case the teeth were situated several inches from the tip of the mandible, while in the type they were at the extreme tip, though still lateral and not terminal as in Ziphius.^†

Again, in the very young specimen of which I obtained only the lower jaw from Kaikoura, the teeth were opposite the hinder edge of the symphysis.^‡

Dr. von Haast has lately described under a new genus Oulodon^§ three specimens obtained by Mr. Hood in the Chatham Islands of a Mesoplodon, which has a row of small teeth in the upper jaw, in a position corresponding to the shallow emargination of the upper part of the ramus of the mandible of the Otago Museum skull (a. fig. 1, pl. XVII). No anatomical description of Ouludon has yet been published, and as the characters of the skulls figured and described by Dr. von Haast were concealed by the dried integument, its exact affinity to the other species of Mesoplodon cannot be detected; but, while the longest of the skulls (No. 1) has the mandible produced to three times the width between the articulations (computed from the orbital width which is given by Dr. von Haast) and the teeth at one-third the length of the mandible from the tip, in both of which characters it again agrees with the Otago Museum skull, the shorter skull (No. 3) has the length of the mandible only twice the articular width, and the tooth at one-fourth the length of the mandible from the tip, thus approaching M. hectori in its proportions.

The presence of rudimentary teeth in the upper jaw of Mesoplodon is certainly a most interesting discovery, but the animals have so seldom been examined in the flesh that it may not prove to be of uncommon occurrence, although it has escaped the notice of all naturalists prior to Dr. von Haast.

Similar teeth in the gum of the upper jaw have, however, been previously recorded for the closely-allied Ziphius cavirostris; but, as Professor Turner remarks in describing a skull of this species found in Shetland, “such teeth are quite rudimentary and functionless, and the presence or absence of such aborted organs ought no more to form the basis for establishing a specific difference, than should the entire absence of teeth both in the upper and lower jaw of the Shetland cranium be a reason for regarding it as a distinct species.”^*

10. Mesoplodon layardi.

Dolichodon layardi, Gray; Cat. S. and W., 353; Hector, Tr. N.Z. Inst., V., 166.

Dolichodon traversi, Gray; Trans. N.Z. Inst., V., 96.

Mesoplodon layardi, Flower; Nature, VII., 368.

Mesoplodon floweri, v. Haast; Trans. N.Z. Inst., IX., 442.

Only five or six examples of this curious and generally supposed abnormal form of ziphioid have yet been met with, and of these I have seen four, (1) a lower jaw from the Cape of Good Hope, collected by the Challenger Expedition, (2) a lower jaw I have already described from the Chatham Islands,^† (3) the complete skeleton in the Canterbury Museum, a very complete anatomical description of which has been given by Dr. von Haast,^‡ and (4) the skeleton in the Sydney Museum, which has been made the type of a new species, Mesoplodon güntheri, Krefft, but which Professor Flower considers to belong to the species now under review.^§

In the last specimen the teeth are not so fully developed into the wonderful strap-shaped arches as in the type, but they are evidently intermediate in their form between it and the triangular tooth of M. sowerbyi. This skeleton has not been yet described, I believe, but Mr. Scott states ^∥ that he has compared it with the drawings of the skeleton of M. sowerbyi given by Van Beneden and Gervais, and cannot detect any essential difference of structure between them. The other species I have seen, although each has received a different specific name, are only distinguished by a slight divergence in the form of the mandible, and the manner in which the large abnormal tooth or rather tusk has been bent or worn, which characters are obviously due to individual variation.

The skeleton described by Dr. von Haast is of a mature and probably an aged animal, and as the other specimens that have large tusks correspond in size, and the osteology in most points agrees with other Mesoplodonts, it is not improbable that it may be only the aged condition of some species already known from immature individuals. Dr. von Haast states

that it is the only ziphioid whale that has three cervical vertebræ anchylosed and four separate;^* but Berardius has this character, and the two skeletons of M. hectori differed in this respect, one having two and the other four vertebræ anchylosed.

Although it is most probable that the hypertrophy of the teeth in this species is only analogous to the overgrown tusks occasionally met with in wild boars, it may be as well for the present to treat it as a character of specific value until further information is obtained about this whale in its earlier stages of growth.

As an aid to the comparison of the various forms comprised in this most puzzling genus Mesoplodon, I have compiled the following table of measurements from the various sources at command:—

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A.—Mesoplodon sowerbyi, Van Beneden.

B.—M. curopœus, Van Beneden.

C.—M. hectori, Tetai Bay, Colonial Museum.

D.—" " Lyall Bay, " "

E.—Skull in Canterbury Museum, no mandible.

P.—Skull in Otago Museum (Pl. XVII).

G.—Oulodon, No. I., v. Haast. In these the total length has been estimated from the other proportions.

H.— " " No. II., " "

I.— " " No. III., " "

K.—Mesoplodon floweri, Haast.

L.—M. layardi, Chatham Islands, Colonial Museum. Breadth computed from distances between articular surfaces.

11. Ziphius cavirostris, Cuvier.

Epiodon chathamiensis, Hector; Trans. N.Z. Inst., V., 164.

Epiodon novœ-zealandiœ, v. Haast; Trans. N.Z. Inst., IX., 430.

Dr. von Haast has given an elaborate description of the second complete skeleton of this whale yet obtained, the first, which is in the museum at