The entire remains measure scarcely 3 inches in length and it is to be doubted if the creature attained a length of more than 4 inches. It is probably a young form, but there are no evidences of external gills. The chevron armature is but poorly preserved, but so far as can be determined it is not different from that of other Microsauria, such as _Amphibamus_. [Illustration: MOODIE PLATE 17 Type of _Saurerpeton latithorax_ Cope. × 1.5. Original in U. S. National Museum.] CHAPTER XVII. THE MICROSAURIAN FAMILY AMPHIBAMIDÆ, FROM THE COAL MEASURES OF MAZON CREEK, ILLINOIS. =Family AMPHIBAMIDÆ new family.= Small, lizard-like, terrestrial or semi-aquatic, megacephalic microsaurians, known from 3 species. The family characters are the huge size of the head as compared to the body, the short, stumpy body with about 25 short dorsal vertebræ, a very short tail, phalanges clawed, pubis of calcified cartilage, sclerotic plates in the orbit to the number of 29 or 30 in each, ventral armature well developed. Teeth anisodont, sharp, conical, non-striate. Two genera are associated in this family: _Amphibamus grandiceps_ Cope, known from three nearly complete skeletons; _A. thoracatus_ Moodie, known from a single incomplete skeleton; _Cephalerpeton ventriarmatum_ Moodie, anterior portion of body and skull. The species are all from the Mazon Creek shales and the family seems unrepresented elsewhere. It may be necessary to compare the Amphibamidæ with the Hylonomidæ when the latter group is better known, but in the light of our present knowledge the two families are distinct. The genera may be distinguished as follows: I. Size small, less than 3 inches in total length, skull with deeply incised tympanic notches (ear-slits) _Amphibamus_ II. Size relatively large, body-length 6 inches or more, teeth distinctly anisodont, skull with nearly even posterior table, limbs very long, ventral armature highly developed _Cephalerpeton_ =Genus AMPHIBAMUS Cope, 1865.= Cope, Proc. Phila. Acad. Nat. Sci., 1865, pp. 134-137. Geol. Surv. Ills., 11, pp. 135-141, pl. xxxii, 1 text-fig. Hay, Proc. Am. Phil. Soc., XXXIX, p. 120, 1900. Moodie, Jour. Geol., XVII, p. 81, fig. 24, 1909. Type: _Amphibamus grandiceps_ Cope.