The publication of the type species of this genus began the researches of Professor Cope on the extinct Amphibia of North America, which he continued for so many years with such excellent results (105-177). The description was based on a single specimen (plate 3, fig. 7) belonging to Mr. Joseph Evans, of Morris, Illinois, who loaned it to Dr. Worthen for the Illinois Geological State Survey (107), in order that it might be described. The type has been destroyed by fire; so I am informed by Mr. L. E. Daniels, of Rolling Prairie, Indiana. There are two other known specimens of the species. One is in the collection of Mr. Daniels and the other No. 794, of Yale University Museum. This genus may be clearly separated from all the other microsaurians by characters which are peculiar to the form. Among these may be mentioned the possession of sclerotic plates in the eyes; the large size of the orbits in comparison with the dimensions of the skull; the short, broad form of the body; the very short tail; the possession of a calcified cartilaginous pubis; clawed phalanges; presacrals 22. The character which places the genus distinctly in the Microsauria is the possession of long, slender, curved ribs, first detected on Mr. Daniels's specimen (plate 14, figs. 1, 2), by Dr. Hay (316). Its stegocephalian characters are evident in every particular of its anatomy the roofed skull, the arrangement of the cranial elements, the presence of a well-developed ventral armature, and the digital formula (4 for the hand and 5 for the foot). The genus _Amphibamus_ was regarded by Cope as a representative of a new order of vertebrates which he called (105) Xenorachia. He later (123) abandoned this, however. Fritsch (251), Zittel (642), and others regarded _Amphibamus_ as a branchiosaurian. The exact position of the form was uncertain until 1900, when Dr. Hay (316) described the long, curved ribs and suggested its place among the Microsauria. He, however (Cat. Foss. Vert., p. 410), made the mistake of including the branchiosaurian family Protritonidæ, under Microsauria, thus confusing the subject further. The genus (462) has not the slightest relationship with the Branchiosauria. =Amphibamus grandiceps Cope.= Cope, Proc. Phila. Acad. Nat. Sci., pp. 134-137, 1865; Geol. Surv. Ills., 11, pp. 135-141, pl. xxxii, and 1 woodcut, 1866. Hay, Proc. Am. Phil. Soc., XXXIX, p. 120, 1900. Moodie, Jour. Geol., XVII, No. 1, p. 82, fig. 24, 1909. Moodie, Kan. Univ. Sci. Bull., VI, No. 2, pp. 343-349, pl. 1, figs. 1 and 2; pl. 5, fig. 3; pl. 7, fig. 1; pl. 11, 12, 13, 1912. Type: Specimen has been destroyed. There is an excellent specimen (plate 4, figs. 5. 6), No. 794 (1234), in Yale University Museum, and another nearly as good in the possession of Mr. L. E. Daniels, of Rolling Prairie, Indiana. Horizon and locality: Mazon Creek shales, near Morris, Illinois.