Thirteen species of theraphosid spiders ("tarantulas") are described as new. Sphaerobothria hoffmani and Aphonopelma seemannz are redescribed and the male 01" S. seemanni is described for the first time . It is argued that the genera discussed here, which are traditionally placed in separa te subfamilies (Grammostolinae and Isehnocolinae) should be grouped . Common features to these genera are the shape of the bulb (distally atenuated and curved ventrally), spermatheea divided in two portions by a deep noteh, and coxa 1 with anterior side covered by conic spinules. The feature formerly used to separa te the two groups is not consistent within genera. Keys, diagnosis and explanations to figures are included in an English Appendi x.