Euphractus Ameghino, in part, 1887, Bol. Mus. La Plata, t. I, p. 26 of separate. Dasypus Amegh., in part, 1889, Act. Acad. Nac. Cienc. Cordoba, t. 5, p. 864. Stenotatus Amegh., 1891, Revista Argen. Hist. Nat., t. I, p. 253. Dasypus Lydekker, 1894, Anal. Mus. La Plata, t. 3, p. 55. Prodasypus Amegh., 1894, Bol. Acad. Nac. Cienc. Cordoba, t. 13, p. 172 of separate. Stenotatus Scott, 1903-5 Princeton Patagonian Exped., vol. 5, p. 80. The genus is very like _Prozaedius_ but differs in having thicker and wider movable plates, in having more rows of plates in the pelvic buckler (11), and in details throughout the skeleton. We found no representatives of the genus, but Ameghino has described a species (no figure), S. (_Prodasypus) ornatus_[22] based on isolated plates. A movable plate measures 18 mm. long by 6-7 mm. wide, while a fixed plate measures 9 mm. long, by 6-7 mm. wide. [Footnote 22: Bol. Inst. Geog. Argen., t. 18, p. 508, 1897.] =Proeuphractus= Ameghino Proeuphractus Amegh., 1886, Bol. Acad. Nac. Cienc. Cordoba, t. 9, p. 208. This genus is seldom found, but is distinguished by Ameghino by the absence of a pelvic buckler, all the plates of the carapace being movable. From the Deseado beds, Ameghino describes two species, _P. setiger_ and _P. laevis_, both based on isolated plates; the former distinguished by having no piliferous perforation in the furrows surrounding the central figure, and with well-developed pits on the posterior margin; while the latter has small piliferous perforations in the furrows and only rudimentary ones on the posterior margin. These features do not seem to me to distinguish species. In addition to the foregoing, Ameghino has made a series of genera and species,[23] _Archaeutatus_, _Amblytatus_, _Isutaetus_, _Sadypus_, _Hemiutaetus_, _Anutaetus_, all based on isolated plates, and distinguished by variations in the central figure and the piliferous pits. I am unable to find a satisfactory basis for distinguishing the genera or species, and feel that, until more complete material is known, it is impossible to say which are valid genera or species. [Footnote 23: Bol. Acad. Nac. Cienc. Cordoba, t. 17, p. 56-66, 1902, no figures.] =Peltephilus= Ameghino Peltephilus Amegh., 1887, Bol. Mus. La Plata, t. 1, p. 25 of separate. Cochlops Amegh., in part, 1889, Act. Acad. Nac. Cienc. Cordoba, t. 5, p. 792. Gephyranodon Amegh., 1891, Revista Argen., Hist. Nat., t. 1, p. 119. ? Anatiosodon Amegh., 1891, Revista Argen. Hist. Nat., t. 1, p. 327. Peltephilus Scott, 1903-5, Princeton Patagonian Exped., vol. 5, p. 88.