Plethodon.–About seven species in North America. This genus has given its name to that of the subfamily, which might with more reason be called Spelerpinae.
P. glutinosus is slaty or bluish-black, with small whitish specks, especially on the sides of the trunk, where they are large and often confluent. The skin is smooth and shiny. Total length about 5 inches, half of which belong to the tail. Holbrook considered this as one of the commonest of the North American newts, and mostly widely distributed, from Ohio to the Gulf of Mexico. It usually lives concealed under stones, but prefers fallen trees, probably on account of the insects upon which it preys. When taken in the hand it gives off a great quantity of slime.
P. erythronotus extends into Canada and is much smaller. Brown or grey above, mostly with a broad, reddish-brown band over the head, back, and tail. The under parts are white, with grey and brown specks.
Autodax s. Anaides.–The large tongue is attached along the median line. The jaws are furnished with few, but surprisingly large, knife-shaped teeth, about ten in the upper and fewer in the lower jaw. The small teeth of the vomers form a chevron-shaped series behind the choanae, those of the parasphenoid stand in one elongated patch. The tail is round; number of toes, five. Three species in Western North America, from California to Oregon.
A. lugubris.–The eyes are very large and prominent. The upper jaw shows a peculiar recess on either side for the reception of the large lower teeth. The skin is smooth, devoid of parotoid glands, but has a strong gular fold. The upper parts are dark brown or lead-coloured, with whitish dots on the sides; under parts white. Total length some 6 inches, about half of which belongs to the tail. The fingers and toes are very rich in subcutaneous venous sinuses.
The habits of these creatures are in many respects peculiar. Van Denburgh[[51]] says of A. iecanus "that it usually moves quite slowly, moving one foot at a time, but is capable of motion surprisingly rapid for a salamander. When moving rapidly, it aids the action of its legs by a sinuous movement of its whole body and tail. The latter is prehensile. Several individuals, when held with their heads down, coiled their tails around my finger, and, when the original hold was released, sustained themselves for some time by this means alone. One even raised itself high enough to secure a foothold. This animal's tail is also of use in another way. When caught, it will often remain motionless, but if touched, will either run a short distance with great speed, or quickly raising its tail and striking it forcibly against the surface on which it rests, and accompanying this with a quick motion of its hind-limbs, will jump from four to six inches, rising as high as two or three."
Ritter and Miller[[52]] have made extensive observations on the life-history of A. lugubris. When wishing to pass from the hand to the table, the creature will frequently execute a well co-ordinated spring and alight on its feet some distance away, instead of falling over the edge in the typical salamander-fashion. This species is nocturnal and entirely terrestrial, and seems to be indifferent even to proximity to water. Rotten stumps and logs are the habitations preferred, and wherever these occur in the region about San Francisco Bay, even though at the places remotest from water, specimens are sure to be found.
The eggs are laid in a hollow under ground, and the female seems to remain curled around them until they are hatched, which takes place in two or three weeks. The specimen observed by Ritter and Miller laid 19 eggs. Each was contained in a gelatinous capsule 6 mm. in diameter, and was firmly anchored to a clump of earth by a narrow peduncle about 8 mm. long. The embryos developed very large gills, each being composed of three broad membranous lobes, the latter being thin and delicate, much expanded, highly vascular and widely confluent at their bases, so that the gills of each side really form one three-lobed mass. Their dorsal surfaces are applied to the inner surface of the egg-capsule. The amount of food-yolk is considerable. The whole larval life is passed through within the egg. Before the young is hatched the gills wither and cease to be functional, and the gill-slits close up. The tail is round, and shows no indication of a fin at any time during the larval period. Newly hatched individuals appeared much distressed when put into water, and were quite unable to swim. They immediately sank to the bottom and remained there until they were removed. The integumentary sense-organs, so well developed in the aquatic larvae of Urodeles, are entirely wanting. When hatched the young creature is about 32 mm. long; its general colour is blackish-grey, finely sprinkled with bluish-silver. During the second year this garb is changed to the dusky brown of the adult, and the fine silver speckling is replaced by much larger and less numerous yellow spots.
Although one of the most terrestrial of Urodeles, this species is lungless, but the skin remains delicately smooth and moist throughout life. According to the observers quoted, the pharynx plays an important part in respiration. From 120 to 180 or even more vibrations are made by the throat in a minute, and in some cases these movements are grouped into series of about 20 to 25 extremely rapid vibrations, with periods between each two series.
Subfam. 3. Amblystomatinae.–Composed of seven closely allied genera, the distinguishing characters of which are the grouping of the palatal teeth and the number of the toes, which varies between 4 and 5. The geographical range of the subfamily extends over the whole of North America and Mexico and over the whole of Northern Asia, from Kamtchatka and Japan westwards to the Ural, and southwards into China. The occurrence of one species, Amblystoma persimile, in the mountains of Siam, makes it highly probable that other species and genera exist in the hitherto unexplored intervening countries.