148 



erectile ruff. Contour-feathers without distinct aftershafts, but having 

 merely a scarcely perceptible small tuft of minute fibrillie 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 ]>lain (in young) or barred (in 

 adult) white beneath, with (in adult) or without (in youug) a black pecto- 

 ral area ; the primaries and tail broadly banded. 



The only bones of either of these genera we have been able to exam- 

 ine are a sternum, with the attached bones, of ThrasaetuSj and a very 

 imperfect skull of 3Iorp]imis. 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 margin 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 

 raj)idly anteriorly, instead of being nearly parallel for their whole 

 length. The only resemblauce to the sternum of Aquila {canadensis) 

 is seen in the broader margin of the keel and its more distinct defini- 

 tion 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 differ- 

 ent from that of Spizaiitiis ornatus. The skull of Morphmis 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 entire palatal surface is 

 wanting, however, in the imperfect specimen before us, and it is prob- 

 able that greater differences may exist in this portion of the skull than 

 in the outlines. 



The two genera composing the group Morplini may be distinguished by 

 the following characters : — 



1. Theasaetus. — Tail about three-fourths the wing. Tarsus less 

 than twice the middle toe, with the frontal and posterior series of large 

 scutellte somewhat interrupted by occasional "dovetailing" of adjoin- 

 ing scales, the posterior series strongly twisted to the outside at the 

 lower portion. Crest-plumes very broad. 



2. MoEPHNUS. — Tail about equal to the wing. Tarsus more than twice 

 the middle toe, the fi'outal and posterior series of large scutellje form- 

 ing 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 fea- 

 tures of the group. 



Its distinguishing features are, abbreviated primaries and greatly-de- 

 veloped supernumerary secondaries; the latter, 18 in number (!), reaching 

 to the end of the primaries. Morplmus 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 — in 

 fact, the whole foot-structure is almost typically aquiline. The genus 

 differs from Aquila, however, in short wing, occipital crest, 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 and occiput destitute of a crestt) ; while the much 

 developed rigid primaries, and shorter tail, approximate this genus more 

 closely to the buteouine series. 



* We have not been able to examiue a skull of Spizaetus. 



t We believe the crest is i^reseut, however, in some Old World species. 



