Credner ([186]), Fritsch ([251, Bd. 1, p. 89, Taf. 12, figs. 1, 4, 15]), and Woodward ([629]) have referred remains of Microsauria discovered in the Coal Measures or lower Permian deposits of Saxony, Bohemia, and Lancashire, England, to the genus Hylonomus. There is much uncertainty as to the validity of these references, due to the uncertain nature of the type of Hylonomus. There are 4 American species of the genus: Hylonomus latidens Dawson, H. lyelli Dawson, H. multidens Dawson, and H. wymani Dawson. All the species are from the Coal Beds at the South Joggins, Nova Scotia.
Hylonomus lyelli Dawson.
Dawson, Quart. Jour. Geol. Soc. London, XVI, p. 274, figs. 14 to 18, 1860.
Dawson, Air-breathers of the Coal Period, p. 44, 1863.
Dawson, Phil. Trans. Roy. Soc. London, 1882, pt. II, p. 635, pl. 39, figs. 1 to 14 and 27.
Dawson, Acadian Geology, 3d ed., 1880, p. 370.
Type: Specimens Nos. R 443 to 445 in the British Museum ([393, pt. IV, p. 223]). Horizon and locality: Coal formation of the South Joggins, Nova Scotia. This species is by far the most abundant ([plate 9]) in the erect trees examined by Dawson. Its characters Dawson ([216]) defines as follows:
"General form lizard-like, with the hind limbs rather larger than the fore limbs. Length when mature, 5 to 6 inches.
"Head somewhat elongate; bones of skull smooth or with microscopic striæ, perfectly united, except at the parietal foramen. Occipital condyle double, and apparently bony. Teeth simple, conical, numerous, about forty in each mandible, and nearly equal, except that a few of the anterior ones are rather larger than the others. The teeth are anchylosed to the jaw in a furrow protected by an external bony plate.
"Vertebræ with cylindrical bodies, slightly concave at the ends. When partly exfoliated they appear hour-glass-shaped, in consequence of the internal cartilage having the form of two cones attached by their apices. Zygapophyses conspicuous above; neural arches united to the bodies of the vertebræ, and with broad neural spines. Dorsal vertebræ with strong lateral processes. Caudal vertebræ apparently simple and cylindrical. Number of vertebræ in neck and trunk about thirty.