FALCONS. 57 



of the remiges of the arm. Tips of the wings at least as long as the tail, if they do not 

 exceed it. 



H. ccerulescens. Twenty-one remiges : the first and second with a slight angular emargi- 

 nation, which extends very far down ; first considerably longer than the third. I was parti- 

 cularly struck by the absence of the circlet of feathers at the apex of the oil-gland, which occurred 

 in at least two of the specimens examined by me. I do not venture to decide whether this is 

 the rule. 



6. With the dorsal stem of the spinal tract enlarged on all sides, undivided and 

 sparsely feathered (Plate II, fig. 5). 



Of this group I am acquainted with two Falcons, which are also very similar in their 

 external appearance, but nevertheless sufficiently distinct. 



1. Falco cacMnnans LINN. Herpetotlicrcs cachinnmis, VIEILL. Galerie, I, PL 19. Eyelids 

 with distinct lashes. Plumage of the head uninterrupted, giving origin above to the spinal tract; 

 below to the inferior tract. The former without anything characteristic as far as the scapular 

 portion ; but the dorsal portion sparsely feathered to the caudal pit, thence diminished and con- 

 tinued as a narrow band along the caudal vertebra? to the oil-gland. It is consequently formed 

 generally as in Rhynchodon, but without the median longitudinal division, and is therefore more 

 sparsely feathered. Lumbar tracts distinctly present, but short and separated from the crural 

 tracts. Inferior tract narrow in all parts; inner branch at the end of the gular portion indistinct; 

 outer branch completely separated from the pectoral stem, somewhat broader than the narrow 

 main stem itself, and far removed from it ; the ventral portion of the main stem removed far 

 outwards, running along the margin, and terminating laterally in front of the anus. Remiges 

 imperfect, so that their number is uncertain : the first very much abbreviated, scarcely measuring 

 two thirds of the second; the latter as long as the fifth; the third and fourth very little longer, 

 but the longest of all ; the sixth somewhat longer than the first, but much shorter than the fifth ; 

 the following ones diminishing still more. The first three with a distinct emargination situated 

 about the middle of the vane, and a corresponding narrowing of the inner half of the vane ; this 

 narrowing is also slightly indicated on the fourth. Tail moderately long, somewhat longer than 

 the folded wings, rounded. Tarsi as long as in F. buteo, powerful, scaled throughout; toes 

 likewise scaled, but with three scutes above the claws. Beak large, particularly thick and high, 

 curved from the very base, most like that of the Buzzards. Nostrils round, with a central 

 cartilage perceptible at the bottom. 1 



2. Falco brachypterus TEMM. PL Col. 116 young, 141 adult. Notwithstanding a great 

 external similarity to the preceding species, this is not merely superficially distinct from it, but 

 belongs to a totally different group. Pterylographically the cervical and scapular portions of the 

 spinal tract, and the entire inferior tract, agree perfectly with those of the preceding bird ; the 

 only thing to be remarked being, that the two stems of the latter are much more approximated 

 to each other, and run along the middle of the belly. But the case is very different with the 

 dorsal part of the spinal tract, inasmuch as this resembles an elongated ellipse (Plate II, fig. 5), 



1 This Falcon is most remarkably distinguished from the Buzzards by the want of the supraciliary 

 bone, in which respect it approaches Rhynchodon, although the beak is quite differently formed ; the 

 feet are less powerful, and the structure of the wings is different. It holds an intermediate position 

 between the two forms. 



