The following four genera, each represented by one or two species only, much resemble each other in the curious shape of the head, which forms a flat projecting snout, used probably for digging in rotten wood in search of insects. There is a peculiar degradation in the extent of dentition of the palatal region. Diaglena and Triprion are the only Hylidae which possess a longitudinal row of parasphenoid teeth. Diaglena petasata of Mexico and D. jordani of Ecuador have, moreover, a transverse row of teeth on the palatine bones in addition to those on the vomer.
Triprion petasatus of Yucatan has parasphenoid and vomerine teeth. The head is a bony casque, with strong superciliary ridges, the skin being extensively ossified. The mouth forms a flat snout, owing to the long projection of the upper over the lower jaw. The skin of the back is smooth brown with darker spots; the under parts are uniform whitish. The male has a subgular vocal sac. Like Diaglena and Corythomantis they possess adhesive discs on the fingers and toes, and climb trees. The total length of this curious creature is 2 inches.
Corythomantis greeningi of Brazil has a similar head. The vomers alone carry teeth, besides of course the maxillae. The pupil is rhomboid. The tongue, as in the two previous genera, is roundish, scarcely free. General colour above olive, with darker freckles; the sides are studded with whitish tubercles; the under parts are whitish. The male is devoid of vocal sacs. Total length 3 inches.
Pternohyla fodiens of Mexico approaches the previous three genera by the curious shape of the head and prominent upper jaw, although these features are not so exaggerated. The dentition agrees with that of Corythomantis and other normal tree-frogs. The fingers and toes are not provided with discs, in conformity with the burrowing, not climbing, habits of this creature. The next following three genera connect the Hylidae with the Cystignathidae. The sacral vertebrae are but slightly dilated.
Fig. 41.–Head of Corythomantis greeningi. × 1. (After Boulenger, Cat. Batrach.)
Acris.–The adhesive discs are very small, the tympanum is indistinct. A. gryllus, the only species, inhabits the greater part of Eastern and Central North America, extending northwards into Canada. It attains a length of 1½ inch. The coloration is very changeable, in adaptation to the surroundings. As a rule it is brown, with a more or less reddish or grey ground-tone, ornamented with dark brown or blackish irregular, longitudinal patches,one of which is bordered with light green,and there is often a light vertebral streak. The legs are cross-barred, the under parts are whitish brown and yellowish. The male has a subgular vocal sac, and its most remarkable feature is the voice, which closely resembles the noise of a cricket or of certain grasshoppers. Holbrook describes it as a merry little frog, constantly chirping like a cricket, even in confinement. It frequents the borders of pools, and is often found on the leaves of aquatic plants, rarely on the branches of such low shrubs as overhang or dip into the water. When disturbed it takes long jumps, and hides at the bottom of the pond. Insects are secured by leaps. It can easily be domesticated, and takes food readily from the hand. Sprinkling them with water never fails to make them more lively and noisy. Appearing in April in great numbers, they are said to vanish early in the autumn for hibernation. The tadpoles are metamorphosed by the end of August.
Chorophilus.–The fingers and toes are provided with very small adhesive discs. The sacral diapophyses are very slightly dilated. About seven species occur in North America, chiefly in the Southern States, one, Ch. cuzcanus, in Peru. Ch. ocularis is the smallest of the frog-kind known, and lives in South Carolina, frequenting damp places, the vicinity of stagnant pools, water-plants or low shrubs, for instance the "myrtle," Myrica cerifera. I once had two of these tiny creatures less than three-quarters of an inch in length. They were very active, and took surprisingly long leaps, jumping distances of 2 feet, but could not be kept through the winter, although they took minute insects readily enough. The head is narrow, long and pointed; the upper parts are of a rich chestnut-brown with a bronzy gloss. The upper jaw is white; a black band extends along the sides of the head and body. The under parts are yellowish white.
Ch. ornatus is another inhabitant of the South-Eastern States; its name refers to the dark brown patches on the back and sides, bordered with golden yellow, upon a reddish-brown ground-tone, while the under parts are silvery white with fine grey spots. This frog, a little more than one inch in length, lives on land in dry places, preferably in corn-fields, has no voice, and, except during the pairing season, carefully avoids the water.
Thoropa.–The fingers and toes are free, the tips simply swollen and not dilated into discs. Closely allied to Chorophilus. Th. miliaris, of Brazil, the only species, has very long toes. The head is broad and flat. The upper, nearly smooth surface of the body is flesh-coloured, with brown marblings; the limbs are cross-barred; the under parts whitish, granular on the belly. The male is devoid of vocal sacs. The total length may be 2 inches. Hensel has published the following notes of this species, under the name of Hylodes abbreviatus. The tadpoles are quite flat, their bellies forming a kind of sucking disc, so that these creatures, even before the appearance of the hind-limbs, can quickly wriggle up vertical walls of stones, provided these are covered with a little water. In correlation with this habit, the root of the tail is not compressed laterally, but is as broad as it is high, and the usual vertical fin is restricted to its distal third. On the proximal portion of the tail the ventral fin is flattened and broadened out so as to form almost the continuation of the peculiar disc-like belly. The anal opening is not a projecting tube, but is a flattened transverse slit.