148 
erectile ruff. Contour-feathers without distinct aftershafts, but having 
merely a scarcely perceptible small tuft of minute fibrillae instead. 
The plumage of these birds is characterized by the broadness of 
the feathers, and the colors by their coarse mottlings or marbliugs 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 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 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 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 
rapidly anteriorly, instead of being 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 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 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 entire palatal surface is 
wantiug, 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 Morphni may be distinguished by 
the 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 
scutellte somewhat interrupted by occasional u dovetailing” of adjoin¬ 
ing 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 scutellte form¬ 
ing each a regular uninterrupted row of broad plates, that behind nut 
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. 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 —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 examine a skull of Spizaetus. 
t We believe the crest is present, however, in some Old World species. 
