OCR Text |
Show 148 erectile ruff. Con tour- feat hers without distinct aftershafts, but having merely a scarcely perceptible small tuft of minute fibrillse instead. The plumage of these birds is characterized by the broadness of the feathers, and the colors by their coarse mottlings or marblings of gray and black on the upper parts, and plain ( in young) or barred ( in adult) white beneath, with ( in adult) or without ( in young) a black pectoral area; the primaries and tail broadly banded. The only bones of either of these genera we have been able to examine are a sternum, with the attached bones, of Thrasaetus, and a very imperfect skull of Morphnus. The former almost exactly combines the characters of the sterna of Aquila and Haliaetus, being much like the latter in all its outlines, the posterior niargiu projecting farthest back in the middle portion, and the keel very high, but the posterior outline is more distinctly sinuated, while the lateral outlines converge very rapidly anteriorly, instead of beiug nearly parallel for their whole length. The only resemblance to the sternum of Aquila ( canadensis) is seen in the broader margin of the keel and its more distinct definition posteriorly, and in the pair of very large oval foramina near the posterior end. In size it agrees with the larger specimens of Haliaetus leucocephalus, but its length is proportionally rather less. It is very different from that of Spizaetus ornatus. The skull of Morphnus is more like that of Aquila than any other with which we have been able to compare it,* in nearly all the details of contour. The eutire palatal surface is wanting, however, in the imperfect specimen before us, and it is probable that greater differences may exist iu this portion of the skull than in the outlines. The two genera composing the group Morphni may be distinguished by thfc following characters:- 1. THRASAETUS.- Tail about three- fourths the wing. Tarsus less than twice the middle toe, with the frontal and posterior series of large scutellse somewhat interrupted by occasional " dovetailing" of adjoining scales, the posterior series strongly twisted to the outside at the lower portion. Crest- plumes very broad. 2. MORPHNUS.-- Tail about equal to the wing. Tarsus more than twice the middle toe, the frontal and posterior series of large scutellae forming each a regular uninterrupted row of broad plates, that behind not twisted to the outside. Crest plumes narrow. The Thrasaetus harpyia is the most specialized form of the aquiline type, possessing in the most exaggerated degree the distinguishing features of the group. Its distinguishing features are, abbreviated primaries and greatly- developed supernumerary secondaries; the latter, 18 in number (!), reaching to the end of the primaries. Morphnus guianensis comes next, with similarly naked tarsi, and the same form of wing and tail as in Thrasaetus, but the crest is more like that of Spizaetus, and the form also less robust. Spizaetus resembles Morphnus, but has feathered tarsi like Aquila- u\ fact, the whole foot- structure is almost typically aquiline. The genus differs from Aquila, however, in short wing, occipital ciest, and elongated tail. Aquila comes next in the series, having the foot and bill of Spizaetus; but the feathering of the head is peculiar ( occipital and nuchal feathers distinctly lanceolate aud occiput destitute of a crestt); while the much developed rigid primaries, and shorter tail, approximate this genus more closely to the buteonine series. * We have not been able to examiue a skull of Spizaetus. t We believe the crest is present, however, in some Old World species. |