Of the OCTODONTIDÆ, an essentially American family at the present day, nearly all the recorded fossil forms are also American. Species of _Echinomys_, _Loncheres_, and _Phyllomys_ were obtained by Dr. Lund from the Brazilian bone-caves, which also furnished him with the remains of a Coypu (_Myopotamus antiquus_), and of an allied form, _Carterodon sulcidens_, distinguished by its having broad incisors with longitudinal furrows and raised ridges. The latter has since been found living in South America. Another species, allied to _Echinomys_, is named by Lund _Lonchophorus fossilis_. The superficial deposits of South America have yielded the remains of two species of _Ctenomys_, one of which is believed to be identical with a recent species. As several species of this family now live in Africa, the occurrence in the eastern hemisphere of fossil forms belonging to it would not be surprising, but the few that have been referred to it are of very doubtful nature. M. Lartet obtained some isolated teeth from the Miocene of Sansan, which he described under the name of _Myopotamus sansaniensis_; and one or two other types (_Aulacodon_, _Adelomys_), from Upper Eocene and Miocene beds, are of very uncertain position. Of the HYSTRICIDÆ, or Porcupines, remains have been obtained in both hemispheres. In the Old World traces of true Porcupines (_Hystrix_) are recorded from the Valley of the Arno, from the Sivaliks, the Pliocene deposits of the Auvergne, from Pikermi, and, on very doubtful evidence, from the Upper Eocene of Lamandine-basse; whilst Dr. Leidy has described two teeth from the Pliocene deposits of Dakota, as belonging to a species (_Hystrix venustus_) allied to the European Porcupine. This determination, if confirmed, would be of great interest, as no true Porcupine now occurs in America. Of the American type, two species of _Sphingurus_ have been obtained from the Brazilian bone-caves; and Professor Cope records a species of the North American genus _Erythizon_ from a similar cave in Pennsylvania. The CHINCHILLIDÆ have left but scanty traces of their former existence. _Lagostomus brasiliensis_ is from the Brazilian bone-caves; and _Megamys patagoniensis_ from the Eocene sandstone of Patagonia. The latter species is founded upon a tibia and rotula, which on comparison seemed to approach most nearly to those of the Rodents of this family, and if the determination be correct it was probably one of the largest species of the order, as the tibia measures about a foot long. _Amblyrhiza_ and _Loxomylus_, are two genera described by Professor Cope from bone-caves in Anguilla Island, West Indies.