mm. Length of skeleton 67 Length of skull 15 Posterior width of skull 15 Depth of tympanic notch 4 Width of tympanic notch 6 Long diameter of the orbit 7 Transverse diameter of the orbit 5.5 Interorbital width 4.5 Diameter of pineal foramen .75 Length of cervical series of vertebræ 9 Length of dorsal series 35 Length of caudal series 13 Length of a centrum of the dorsal series 1.5 Length of dorsal rib 3.5 Length of arm 20 Length of humerus 7 Length of radius and ulna 4 Width of carpal space 3 Length of third digit 5 Length of leg 25 Length of ilium 3 Length of femur 9 Length of tibia and fibula 5 Length of carpal space 4 Length of 1st digit 3 Length of 2d digit 4.5 Length of 4th digit 7 3 ventral scutellæ in 1 mm. =Amphibamus thoracatus Moodie.= Moodie, Proc. U. S. Nat. Mus., 40, pp. 431-433, fig. 2, 1911. Moodie, Kans. Univ. Sci. Bull., VI, No. 2, pp. 347-349, pl. 5, fig. 2, 1912. Type: Specimen No. 4306, U. S. National Museum. Horizon and locality: Mazon Creek shales, near Morris, Illinois. The type is a part of the collection of Mr. R. D. Lacoe, in the U. S. National Museum. The fossil is very poorly preserved, but the remains are to be seen on both halves of the nodule, so that considerable can be made out as to its structure. The chief diagnostic characters which will at once distinguish the species are the elongate arm, large interclavicle, shape of the vertebra, and triangular skull.