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. "Ribs long and curved, with capitulum and tuberculum, cartilaginous within. "Anterior limb slender, humerus with distinct keel; radius and ulna separate; toes four or five. "Posterior limb with well-developed femur; tibia and fibula shorter, separate; toes five, somewhat long and slender. "Pelvis large, composed of ilium and ischium." Interclavicle and numerous scutellæ are present. Upper surface protected with imbricated horny scales. In front two rows of horny tubercles and plates, with epaulettes composed of bristle-like fibers projecting from the skin. The animal possibly fed on insects, as is indicated by the coprolitic matter associated with the remains of the species. The following measurements are given by Dawson for the largest individual discovered: Length of head about cm. 2 Length of neck " " 1.3 Length of trunk " " 7 Length of posterior limb to heel cm. 3 Length of mandible " 1.8 Teeth, 5 in 1 mm. Length of rib cm. 1.3 Length of humerus " 1.4 Length of femur " 1.8 Length of tibia " 1.2 Length of body of vertebra mm. 2.5 =Hylonomus latidens Dawson.= Dawson, Phil. Trans. Roy. Soc. London, 1882, pt. II, p. 637, pl. 39, figs. 18-22. Dawson, Proc. and Trans. Roy. Soc. Canada, 1895, p. 74. Type: Specimen No. 3061-1, Peter Redpath Museum, McGill University. The British Museum (393, pt. IV, p. 224) also has a specimen, No. R 447.