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Show 232 ME. H. O. FORBES ON THE [Feb. 28, riorly. In A a line drawn through the meatus auditorius at right angles to the length of the rostrum transects it posteriorly to its crest, while in older specimens such a line falls anterior to the supra occipitofrontal suture. The crest of the vertex is wider, and the bones which meet there (the nasals, frontals, supraocci-pitals, maxillaries, and premaxillaries) articulate very loosely with each other. In the youngest form I have examined the nasals lie vertically between the ends of the premaxillaries, the right nasal being on, and the left beneath their level in the vertex ; but as these whales advance in age the nasals sink more deeply between the crest of the premaxillaries, and with the frontals are tightly squeezed together between the premaxillary, maxillary, and supra-occipital bones. The nasal ends of the premaxillaries are less vertical, lower aud less everted, and the asymmetry between their right and left portions in the younger individuals is but slightly marked, the right side, however, being always a little larger than the left. The inner borders of the maxillaries are parallel, presenting a gibbosity (cf. fig. 1, gib) opposite and extending anteriorly to the maxillary foramina. These gibbosities, which become more marked with age, are but slightly observable in Van Beneden's figure and in A, are already more prominent in the Royal College of Surgeons example, and still more so in the intermediate specimens. As I have remarked above, they occur over tbe intervals in which the vomer does not show on the palatal surface. The premaxillary foramina lie behind those of the maxillary, as usual in this species, and are situated-the right ^ inch and the left ^ of an inch- anterior to a line joining the anteorbital notches, and also anterior to the forward termination of the ethmoid bone. A line drawn thus in the Kaiapoi specimen (I) runs obliquely between the two pairs of foramina, but nearer to the premaxillary foramina than in the type. In the Canterbury Museum example (H) it touches the posterior margins of the right maxillary foramen, and the two pairs are situated nearer than in the type (which closely resembles Flower's haasti in this respect) or in the Kaiapoi specimen, being in the case of the nearest *25 inch distant (as they are unsym-metrical, the right one of the two is slightly farther apart); in the type they are 1'90 and in the Kaiapoi specimen T25 inch apart. In the Royal College of Surgeons example of M. grayi such a line passes midway between the pairs, while in Flower's M. australis it traverses the left premaxillary foramen and comes very near the anterior margin of the right. In the older Otago Museum specimen (F) the right maxillary foramen is f-$ inch more posterior to the line than the left, and the pairs are distant, the right 1-^j- inch and the left 1| inch. It is evident, therefore, that during growth there is a movement of the maxillaries and premaxillaries upon each other, which may not improbably have something to do with originating the proliferation of osseous tissue in the premaxillaries and vomer. In full-grown specimens these foramina are posterior to such a line and are more nearly opposite the anterior termination of the mesethmoid. The floor and sides of the mesorostral |