The following genera are small newt-like creatures of the Carboniferous age of Europe and North America. In Keraterpeton of Bohemia, Ireland, and Ohio, the dermal scales were restricted to the under parts; and the ribs were rather long, reaching half way round the body. Gills have not been observed. K. crassum, a European species, reached more than one foot in length, two-thirds of which fall to the tail. The ventral side is covered with a most elaborate armour, which consists of about eighty chevron-shaped rows of little scale-shaped nodules. The epiotic bones end in strange processes, carrying a pair of spikes, giving the skull a "horned" appearance, hence the generic name. Urocordylus is an allied genus.
Sub-Order 2. Aistopodes.–Body snake-like and without any limbs, hence the name ἄιστος, unseen; ribs long, and reaching half way round the body; from Carboniferous strata in Ireland and Bohemia, with allied, or perhaps identical forms in Ohio. Dolichosoma longissimum possessed more than 150 vertebrae, and was about a yard long. The epiotics end in obtuse projections, recalling those of Keraterpeton. These marvellous creatures had strange appendages, extending from behind the sides of the head, which were possibly the supports of external gills; since the upper end of one of the visceral arches, probably the hyoidean arch, is attached to the labyrinthic region, and from this arch starts a bony rod which carries long skeletal filaments. The body seems to have been naked.
Ophiderpeton had a compound ventral shield, while the skin of the back contained granular scutes. Although the Aistopodes have, not without reason, been looked upon as greatly resembling the Coeciliae or Apoda in organisation, especially in that of the vertebral column, the total absence of any other fossils which might bridge over the enormous gulf between the Coal Age and recent times, makes the attempt to derive the Apoda from these creatures very hazardous.
Order II. STEGOCEPHALI TEMNOSPONDYLI.
Mostly with rather long ribs and with chiefly ventral armour.
Chelydosaurus from the Lower Red Sandstone of Bohemia was 3 feet long, and possessed a beautiful, complicated, ventral armour, consisting of about sixty chevron-shaped rows, about three times as numerous as the vertebrae in the corresponding region. Sphenosaurus from the same strata and localities must have been 2 yards long. The trunk-vertebrae of both these genera were composed of four pairs of arcualia. Trimerorhachis from the Permian of Texas is very imperfectly known, but its trunk-vertebrae, as the name implies, consist of three pairs of separate arcualia, one of which, the interdorsal pair, tends to form a kind of centrum.
Dissorophus multicinctus, also from the Permian of Texas, has been described by Cope[[40]] as a "Batrachian Armadillo," and considered allied to Trimerorhachis. Ten vertebrae are known, of an aggregate length of 93 mm.; the length of the creature was perhaps one yard. The neural spines are elevated, and the apex of each extends in an arch on each side to the ribs. These spinous branches touch each other, forming a carapace. Above, and corresponding to each of them, is a similar dermal and osseous element, which extends from side to side without interruption in the median line, forming a dermal layer of transverse bands which correspond to the skeletal carapace beneath it. This creature remotely approaches the genus Zatachys, Cope, where a dermosteous scute is co-ossified with the apex of the neural spine. The systematic position of this genus is at least doubtful.
Archegosaurus decheni from the Lower Red of Germany, known by many well-preserved specimens, reached a length of 4 or 5 feet. The trunk vertebrae are tri-partite, those of the tail quadri-partite, like those of the trunk of Chelydosaurus. Young specimens show traces of gill-arches. The thoroughly terrestrial walking limbs have four fingers and four toes; the arrangement of the tarsalia, most of which are ossified, lend support to the view that the morphological axis went through femur, fibula, intermedium, the centralia, the second distal tarsale, and the second toe. The dentine and enamel of the teeth are much folded, and this feature, which applies to most members of this Order, to a lesser degree also to others, has caused them to be comprised under the name of Labyrinthodonta. The upper surface of the head shows very characteristically arranged grooves, which probably contained slime-canals and possibly sensory organs.
Actinodon and Euchirosaurus are closely allied forms, chiefly from the Lower Red Sandstone of France; Gondwanosaurus occurs in the Permian of India.
Order III. STEGOCEPHALI STEREOSPONDYLI.