_(?)Platystegos loricatum_ Dawson, Nova Scotia. Genera and species of uncertain position: _Amblyodon problematicum_ Dawson, Nova Scotia. _Proterpeton gurleyi_ Moodie, Illinois. _Brachydectes newberryi_ Cope, Linton, Ohio. Order Stereospondylia Zittel, 1887. Coal Measures (?) and Triassic. Family _Mastodonsauridæ_ Huxley, 1863. _Mastodonsaurus_ sp. indet., Kansas. The above list of species is interesting in that it shows the diversity of structure among the Coal Measures Amphibia. There are at present 88 species known, many of them incompletely, divided among 17 families and 5 orders. The majority of the species are from the Linton Coal Measures, there being 50 species described or indicated from these beds. The Mazon Creek shales have furnished 10 species; Nova Scotia 18 species; the remainder of the species are from various localities. CHAPTER VIII. DEFINITION OF THE CLASS AMPHIBIA LINNÉ, 1758, DEVONIAN TO RECENT. (World-wide distribution.) Cold-blooded vertebrates; aquatic or partially terrestrial in habit; body scaled or naked or partly covered with bony or horny plates; abdomen sometimes protected by closely packed scutes, scales, or rods; skull completely roofed-over or with a single vacuity; pterygoid-palatine arch complete or wanting; stapes always present; two occipital condyles, sometimes cartilaginous; skull bones pitted and grooved by the lateral-line canals, or smooth and lateral-line canals wanting; parasphenoid well developed; palatine vacuities, large, small, or absent; basioccipital partly or entirely cartilaginous; sclerotic plates present or absent; mouth always terminal; teeth sharply conical, smooth, or plicated, with walls sometimes extremely complicated by the infolding of the dentine and enamel. Vertebræ procœlous, opisthocœlous, amphicœlous, amphiplatyan, temnospondylous, stereospondylous, or cartilaginous; notochord often persistent; column divisible into cervical, dorsal, and caudal series; cervical series, so far as known, always short; dorsal region long or short; a single sacral or two; caudal series short, very long, or absent. Pectoral girdle composed of an osseous scapula, cleithrum, clavicle, interclavicle, and coracoid with various relations; sternum undeveloped; pectoral girdle of membrane bones; in Triassic forms producing the effect of a plastron on account of the high development of the clavicles and interclavicle. Pelvis usually composed of an osseous ilium and ischium; pubis when osseous surrounded by large amounts of cartilage, usually cartilaginous, sometimes calcified. Limbs ambulatory, natatory, or wanting; limb bones composed either entirely of perichondrium or of perichondrium and a small amount of endochondrium; radius and ulna, and tibia and fibula free or fused. Digits 3 to 5, usually 4 for the hand and 5 for the foot.