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Show 26 PROF, D'ARCY W. THOMPSON ON T H E [Jan. 17, well-marked. The quadrate articulation is scarcely separated in the dry skull from the tympanic cavity. The " suprameatal area " is rather large and faces outwards; it is in fact unusually conspicuous, though vastly less developed than in Nestor. The inner head of the quadrate is small, widely separate from the outer, and bent sharply inwards; the pterygoid condyle is imperfectly separate from the mandibular. In the mandible the marginal surface of articulation with the body of the quadrate is very conspicuous, and the edge of the mandible is here bent outwards. A small mandibular fontanelle is present; the angle of the jaw is short but pointed. As in Cockatoos generally, the interorbital vacuity is small and rounded. In one point, not among those chiefly considered in this paper, the skull of Calopsittacus differs from its congeners : between the anterior rami of the palatines there are visible (as in Psittacus) two long processes descending from the posterior portion of the maxillary bones ; these are the " median processes of the inferior margin of the postaxial surface of the prosopium," in Dr. Mivart's description of Psittacus. They are, as a rule, small or obsolete in the other Cacatuidse. It is clear that the skull of: Calopsittacus, though at first sight very similar to, is different in several respects from, the true Cacatuine type. It is possible that these differences involve resemblances to the Platycercini, and this question will be further discussed below. Family NASITERNINJJ. I have examined the tiny skull of N. pygmcea in an example unfortunately not full-grown, belonging to the Museum of the R. College of Surgeons. It is impossible to rest much weight on this beautiful but imperfect little skull. The orbit is exceedingly incomplete, the prefrontal process being very short (the prefrontal bone is not yet quite co-ossified with the frontal, and is in close connection for an almost equal extent of contact with the nasal). The postfrontal process is also small and scarcely prominent; the squamosal process, on the other hand, is long and slender and directed obliquely downwards. The posterior border of the auditory meatus is nearly straight. The suprameatal tubercle and its subjacent groove are both well marked. THE MACAWS. The great Blue Macaws differ, as is well known, from the rest in certain of their cranial characters. In Anadorhgnchus hgacin-thinus (fig. 18, p. 27) the orbit is incomplete, the prefrontal process terminating in a sharp point below the middle of the orbit. The postfrontal process is of moderate size, short but massive; the squamosal process is rather small, and united nearly to its tip on the inner side by a bridge of bone to the edge of the temporal fossa. The auditory meatus is wideandapproximately square in outline; the posterior and superior recesses of the tympanic cavity are scarcely |