The genus was established by Ameghino for forms similar to _Steiromys_ of the Santa Cruz, but antedating that time. I confess I can see but little difference between _Steiromys_ and _Eosteiromys_, but the latter is as yet known only from isolated teeth and as in general it would be expected that there should be a generic difference, we may let this genus stand representing rather a prophecy than the facts as yet known. The upper teeth are brachydont, the crown being on the same general plan as in the foregoing genus, _i. e._, it is divided into an anterior and posterior lamina by a deep external median fold and by a shorter oblique internal median fold. The anterior lamina is subdivided by two external furrows, a lesser anterior and a larger posterior; while the posterior lamina is subdivided by a single external furrow; so that this tooth has four folds, furrows, or pits on the external side separating five lobes; while on the inner side there is but the one oblique fold separating two lobes. =Eosteiromys medianus= Ameghino [Illustration: Fig. 130. Right upper molar, 2 × 4/1.] ? E. medianus Amegh., 1902, Anal. Mus. Nac. Buenos Aires, ser. 3, t. 2, p. 129. The genus is based on a single, though entirely characteristic, upper molar. We found just one tooth of the species, also an upper molar. It is described above, under the genus. The measurements are: Upper molar 2, length 4 mm., width 5 mm. CHAPTER XIV EDENTATA The scarcity of edentates in the Deseado beds is in striking contrast to their abundance in the Santa Cruz formation. Whereas in this latter horizon over half of the finds are edentates, in the Deseado only eight per cent. of the total collection belong to this group, and this is doubtless a larger proportion than these animals represented in the fauna; for the hundreds of small plates in a carapace, when scattered greatly, increase the chance that some part of an individual will be found, and most of the eight per cent. of finds are single plates. Most of the plates found represent armadilloes, our collection containing but one plate of a glyptodont, and no gravigrades. Ameghino’s collections present about the same relations, but in the repeated trips he found a few more traces of glyptodons and a very few gravigrades. This scarcity of edentates can not be taken to mean that they were not developed, for they are a peculiarly South American group, and as they were developing somewhere into their great complexity, I take it to mean that the climatic conditions were unfavorable in this particular section. As noted above, all previous finds have been isolated plates. We were fortunate enough to find one specimen consisting of a carapace with ten rows of movable plates in place, and parts of four rows of the pelvic buckler together with over fifty isolated plates. A second specimen had some fifty associated plates which were mostly from the pelvic buckler. Dasypoda