Apparently the palatal ridge develops with the gradual growth of the bill, and becomes fully functional shortly after the immature bird is left by its parents to its own resources in securing food. It seems to be fully grown in all by the middle of September. In many adult specimens the ridge shows signs of heavy wear from the nearly constant use to which it is put. In some the cutting angle was well rounded in front from constant abrasion, while in others the anterior margin had become irregular and broken. In one specimen the thin lower margin of the compressed keel was entirely worn away, leaving a low rounded projection in which the two sides of the fold by which the keel had been formed were clearly visible, with a line of separation between them. It was interesting to note that the palatal ridge was usually well worn in old adults, taken in late fall or early spring, belonging to the northern races (Quiscalus q. quiscula and Q. q. æneus) while little or no wear was apparent in similar specimens of the southern form (Q. q. aglæus) from South Carolina and Florida. The data available from the examination of a small number of stomachs of this form from Florida show a preponderance of insects and fruits with very little mast or grain, a fact of interest, but one that is not fully substantiated as the material available is small.
Among near relatives of Quiscalus quiscula a slightly developed palatal ridge was encountered in Megaquiscalus macrourus, where the projection was broad and well rounded posteriorly, and narrow in front with the lower margin acute, forming a sharp keel. In some specimens seen this keel was slowly reduced until it merged smoothly with the palatal surface in front. In others the anterior margin was obtusely declivous. The obtuse anterior cutting angle projected below the margins of the tomia for nearly a millimeter in a few individuals, and in these occasional specimens the resemblance was striking to those bills of Quiscalus in which the ridge was most poorly developed. Juvenile specimens of Megaquiscalus m. macrourus from Fort Clark, Texas, that had been collected just after they had left the nest, had the palatal ridge already well indicated though only about one-half developed. In the slender-billed forms known as Megaquiscalus tenuirostris and M. nicaraguensis the palatal keel was much as in M. major though slighter and less pronounced.
In Blackbirds belonging to the West Indian group known as Holoquiscalus a raised line was also more or less developed. In general the growth was similar to that in Megaquiscalus as the posterior portion was broad and rounded, while anteriorly the ridge was narrowed and the lower margin became acute. There is some variation in the size of this anterior portion; in a few the crest is obtusely declivous in front, approaching the condition found in Quiscalus, but never with the keel produced so that it projects below the plane subtended by the cutting edges of the tomia.
The discovery of a peculiar knoblike process on the palate of the mexican orioles belonging to the species Icterus gularis was one of the really surprising discoveries made during a more or less cursory examination of the palate in various species and genera of Icteridæ picked out at random, and it was the finding of this structure in an Oriole that led to a detailed examination of all of the material available. In Icterus gularis the palatal ridge is from 1.2 to 1.5 millimeters high at its anterior end [(Fig. 2)]. The entire structure is broad and somewhat flattened. The ventral surface is slightly rounded, the sides slightly sloping, the sides and lower surface joining at a sharp angle. In front the ridge is abruptly truncated at its ventral margin where there is sometimes a slight tooth or projection. Below this point the anterior surface slopes abruptly, and then passes over into the roof of the palate. The ridge is about two millimeters broad, and there is a slightly indicated raised line on the ventral surface for three-quarters of its length behind. From this description it may be seen that this blunt projection is entirely different from the sharply keeled ridge found in Quiscalus.
Fig. 2. Head of Icterus gularis yucatanensis.
b. Palatal knob (about natural size.)
Examination of other orioles shows that Icterus gularis stands alone in respect to this development as there is nothing found in other species that approaches it save for a broad, low, rounded projection, slight but distinct, that is found on the palate in Icterus xanthornus. In Icterus laudabilis and I. prosthemelas there is a very slightly raised median ridge developed on the posterior part of the roof of the mouth. In twenty-eight other species belonging to this genus the palate exhibits no peculiarities worthy of mention. This structure in the bill in Icterus gularis is constant in its presence, and serves as a trenchant character distinguishing it from other orioles, or in fact from any other members of the Icteridæ that have been available for examination. The differences pointed out above, together with others of lesser importance, seem to be of generic value. It is therefore proposed to recognize for this species the genus name
Andriopsar Cassin.[16]