42 PEOP. D'aRCY W. THOMPSON ON THE [Jail. 17, 



region shows does not amount to an indication of affinity between 

 the two outlying forms. On the whole, the facts in our possession 

 seem to eontirm the right of both genera to represent separate 

 families very distinct from the other Psittaci, and there is more 

 evidence in the skull of Stringops than in that of Nestor of low or 

 primitiA^e characters. In spite of its complete orbit I am inclined 

 to think it the lowest or least modified of a highly modified group, 

 and to look upon Nestor as an aberrant but less primitive form, to 

 which, however, I cannot assign a direct connection with, or deri- 

 vation from, any other known genus. 



The Cockatoos are for the most part distinguished by a complete 

 orbit, and by the fusion of the suborbital bar both with the post- 

 frontal and with the squamosal process, so that a bridge is formed 

 across the temporal fossa {cf. Garrod, P. Z. S. 1874, p. 594) ; where 

 the temporal fossa is incompletely bridged, as in Microglossa and in 

 Oacatua ducorpsii, a posterior ramus extends backwards, apparently 

 from the postfrontal part of the suborbital bar, to bridge it in- 

 completely. The shaft of the quadrate is stout, the region bearing 

 the jugal cup is elevated, and the external or subjugal articular 

 surface comparatively well-marked. The interorbital septum is 

 deep and truncated or indented anteriorly. The auditory meatus 

 is on the whole wide, and its posterior border is always very near 

 to the occipital ridge. The external iiares are round, and com- 

 paratively small, sometimes, as in Microglossa, very small indeed. 



Calopsittacus is, in the character of its orbital ring, thoroughly 

 Cacatuine ; but it differs in its larger and more oval nostrils, and 

 in a greater narrowing of the auditory meatus by reason of the 

 ingrowth of its posterior wall, which leads to an extension of the 

 interspace between the meatus and the occipital ridge. Cacatua 

 roseicapilla forms in both respects an intermediate stage. 



The only other Parrot in which the temporal fossa is bridged by 

 bone, so far as I know, is Melopsittacus, though here the squamosal 

 process is much broader and flatter, and the temporal fossa much 

 smaller than in Calopsittacus. The two skulls, however, show a 

 strong resemblance one to another. 



With the exception of Melopsittacus, the whole group of Austra- 

 lian Parrots united under the name Platycercince agree, so far as I 

 have examined them (and I particularly regret the want of Pezo- 

 porus and Oeopsittacus), in several distinctive characters. The 

 Australian genera Polytelis, Aprosmictus, and Pyrrhulopsis (and I 

 expect Ptistes also) agree so perfectly in cranial characters with the 

 Platycercince, that I do not doubt for a moment the necessity of 

 removing them from the Palceomithince and uniting them with the 

 other Australian genera. The leading character in all these forms 

 is the presence of a deep groove or excavation at the base of the 

 squamosal process, the area overhung by the suprameatal process 

 being confluent with the temporal fossa. The auditory cavity is 

 clearly bounded in front and separated from the region of the 

 quadrate articulation by a bar of bone confluent above with this 

 region in front of the suprameatal process. There is further. a 



