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Show 30 PROF, D'ARCY W. THOMPSON ON T H E [Jan. 17, postfrontal process is in both cases very small, while the squamosal one is of large size. The auditory meatus is narrow, especially in Myopsittacus. A mandibular foramen is present and large in Brotogerys, absent in the others; the ramus of the mandible is in both longer and its angle less truncated than in the Conures. The nares in Brotogerys are even larger than in the Conures, and separated by a very narrow bridge of bone; in Myopsittacus, on the other hand, they are unusually small and wide apart. Family PIONIN^;. Of this group I have studied Chrysotis cestiva (fig. 22), Pachynus bracliyurus, Pionus menstruus and P. maximiliani, Caim melano-cephala (fig. 24, p. 31), and Pceocephalus fuscicapillus (fig. 26, p. 31). Of these, Chrysotis and Pionus are markedly different from the rest. In Chrysotis the orbital ring is complete, by the fusion of the pre- Fig. 22. Chrysotis cestiva. Fig. 23. Quadrate bone of Chrysotis cestiva. orbital and postorbital processes, and the bar thus formed is strong and broad, and forms with its lower border an abrupt descending angle opposite to the extremity of the squamosal processes, which closely approaches it. The latter is broad and massive, and'similar in shape to that of Conurus; the temporal fossa between the postfrontal and squamosal processes is deep, but unusually narrow. The auditory meatus is wider, its superior and inferior notches are broad and rounded, and the ridge separating it from the quadrate articulation is low and indistinct. The prootic articular surface is |