OCR Text |
Show 162 DR. J. MURIE ON GEOPSITTACUS OCCIDENTALIS. [Feb. 27, and the digits are concerned. The first form is no doubt the stouter-limbed of the two. Platycercus approaches nearer to them than docs Euphema. The same remarks apply to the claws. Curiously enough, the claw of the fourth digit in 'Geopsittacus slightly surpasses in length that of Pezoporus, although the remaining claws are the shortest. While discussing the external characters, I shall just add a few remarks bearing somewhat upon the physical contour of Geopsittacus. I had the opportunity of comparing the body of this bird, when disrobed of skin and feathering, side by side with those of Platycercus flaveolus, Lorius chlorocercus, and Calopsitta novee-hollandice in a similar condition. It then appeared that Geopsittacus and Platycercus were nearly alike with regard to their muscular development and proportions of depth to length of body and keel. The former, however, had very slightly the advantage over the latter in vertical depth posteriorly. Lorius chlorocercus, with a much longer body than any one of the other species, had less vertical depth anteriorly than Platycercus and Geopsittacus, and only slightly more than Calopsitta. O n the other hand, while the three last-mentioned genera more nearly agreed in the depth of the body behind, Lorius differed from them all in its being much greater. These limited observations would seem to indicate that the chest or wing-giving power is greatest and nearly alike in Geopsittacus and Platycercus, whereas Lorius and Calopsitta are stronger relatively towards the rump and in the abdominal region generally. Expressed in antithesis it points to volatorial powers versus scansorial habits. Circumstances, I regret, only permitted me to examine the osteology through the sternum, which possesses characters in common with those of the Parrot tribe. Its body is elongated in shape (1"*7), narrowest (0"*65) and deepest forwards, shallowest and expanded (0"*85) behind. The middle xiphoid region * shows a tendency to be produced ; but this is so slight as barely to break the regularity of the arch of the posterior border. There is a large fenestra on each side, of an oval figure. These, in the specimen in question, have an irregular margin, from partial filling-in of delicate osseous material. At an earlier stage, therefore, the fenestras must have been proportionally larger and more ellipsoid in contour. The keel is large and deep (0""6 anteriorly) and has a gentle but not greatly projecting anterior curvature, fashioned after the manner of the prow of a steam-ram. There are six pointed serrations, or costo-condyles, for the attachment of as many sternal ribs. * In the description of the sternal bones, I have throughout followed the terms adopted by Mr. Parker in his recent " Monograph on the Structure and Development of the Shoulder-girdle and Sternum in the Vertebrata," Kay Soc. 1868. The breadth of his researches and the sequence in the developmental condition of the parts examined by him give us a more trustworthy basis than heretofore. |