_Hylonomus lyelli_ Dawson, Nova Scotia. _latidens_ Dawson, Nova Scotia. _multidens_ Dawson, Nova Scotia. _wymani_ Dawson, Nova Scotia. _fritschii_ Gein. and Deichm., Saxony. _geinitzi_ Credner, Saxony. _(?) pictus_ Fritsch, Bohemia. _wildi_ Woodward, England. _Smilerpeton aciedentatum_ Dawson, Nova Scotia. _Hylerpeton dawsonii_ Owen, Nova Scotia. _intermedium_ Dawson, Nova Scotia. _longidentatum_ Dawson, Nova Scotia. _Fritschia curtidentata_ Dawson, Nova Scotia. =Genus HYLONOMUS Dawson.= Dawson, Quart. Jour. Geol. Soc. London, XVI, p. 274, figs. 14-18, 1860 Dawson, Air-breathers of The Coal Period, p. 44, 1863. Dawson, Phil. Trans. Roy. Soc. London, 1882. pl. 11, p. 634. Credner, Zeit. d. deutsch. geol. Gesell., 1890 (IX Theil, die Stegocephalen und Saurier). Type: _Hylonomus lyelli_ Dawson. The genus _Hylonomus_ is a very important one from a taxonomic viewpoint, since it was regarded by Dawson (216, p. 635) as the typical genus of the order Microsauria, the most abundant group in the Carboniferous. Unfortunately the species of the genus _Hylonomus_ are known only from fragmentary remains. I have reproduced in plate 9 Dawson's figures of the remains of _Hylonomus_ as published by him in 1891. Dawson (216) gave, in 1882, the following definition of the genus _Hylonomus_: "Form lizard-like, with the posterior limbs somewhat large in proportion to the anterior. Size, small. Mandibular and maxillary teeth numerous, small, conical, pointed. Palatal teeth minute. Abdominal scales oval." [Illustration: MOODIE PLATE 9 _Hylonomus lyelli_ Dawson. 1, maxillæ and skull bones; 1_a_, sternal bones; 2, mandible; 3, humerus, ribs, and vertebræ; 4, posterior limb; 5, pelvis; 6, caudal vertebræ. Nearly natural size. Erect tree, Coal formation, South Joggins, Nova Scotia. Photograph by Dawson, published through the courtesy of Dr. Arthur Willey. Original in the British Museum.] 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.