RHYNCHODON. 55 



sternum and the outer margin of the pectoralis major, and occur broader than usual upon the 

 ventral surface, upon which, however, they terminate before reaching the pelvis and the anus. 



3. The hypoptcrum, which is generally confined to the inner surface of the upper arm, is 

 continued upon the breast, and forms a row of large contour-feathers close to the outer margin of 

 the pectoral tract. 



4. The spinal tract, as far as the shoulder, is without any distinguishing marks ; but its 

 dorsal part consists, at first, of two rows of single feathers, which issue, parallel to each other, 

 from the points of the fork, become broader in proportion as they increase in length, and only 

 coalesce immediately in front of the oil-gland, to form a short, broad, main stem, which has 

 contour-feathers sprinkled beside it. 



5. The lumbar tracts are probably entirely wanting. 



6. The oil-gland is remarkably large, probably larger in proportion than in any other bird ; 

 it is cordate, with a short apical part with two orifices ; each half of the gland has a large, deeply 

 penetrating, wide cavity, of which the wall consists of a very thick membrane. 



7. In the wings I find twenty-nine remiges, which is also a comparatively large number. Of 

 these the first is somewhat longer than the fifth, and the second and third exceed all the others 

 in length. The first three have an angular emargination -on the inner half of the vane, and are 

 diminished in size from this point ; the fourth exhibits a trace of this. The ala spuria has a 

 thin, straight claw, and, at least sometimes, Jive feathers. 



8. Rectrices short, reaching only to the tips of the folded wings. 



2. Falcons of which the pectoral tract emits a completely or partially free exterior branch. 



a. With the dorsal portion of the spinal tract deeply divided, and each limb dilated 

 exteriorly. 



Here belong all the Nolle Falcons, which, as they differ more than any other group from the 

 other Hawks, I regard as forming a distinct genus, for which I propose the name of Bhytichodon. 

 Judging from an examination of Eh. islandicus, pereyrinus, (Bsalon, subbuteo, tinnunculus, tinnuncu- 

 loides, ri/flpes, concolor, TEMM., and c&rulescens LATH., they present a very great and complete 

 agreement in the pterylosis, the chief peculiarity of which is expressed in the above-mentioned 

 form of the dorsal portion of the spinal tract and the jugular portion of the inferior tract (see 

 PI. II, fig. 6). The following points appear to me worthy of notice : 



The down-feathers are white or gray, remarkably soft, mould-like, and clinging together 

 when pressed ; they all have a short main shaft and an aftershaft of equal length. They are 

 sometimes entirely wanting in some spaces, as, for example, on the lateral neck-spaces ; they are 

 everywhere sparse. 



Contour-feathers with a considerable, but, as usual, merely downy aftershaft; main shaft 

 rigid ; barbs for the most part pennaceous. 



Head uniformly feathered, but with the region of the eyes naked, and the lores clothed 

 with setiform feathers arranged in a whorl. 



Spinal tract with robust feathers throughout ; it starts nearly from the occiput, and divides 

 in a long fork between the shoulders. The dorsal portion commences with two parallel rows of 

 simple feathers between the fork, and becomes perceptibly broader by the addition of new rows 

 on the outside of each of the ^original rows, but at the same time more sparsely feathered. The 



