Suborder 2. =Typotheria=: teeth hypsodont lower molars with the anterior crescent shorter than the posterior; squamoso-periotic region inflated; limbs elongated in varying degrees; pes plantigrade to semi-plantigrade; digits 5-4 or 4-4. Suborder 3. =Toxodontia=: teeth brachydont to hypsodont; lower molars with the anterior crescent shorter than the posterior; squamoso-periotic region inflated; limbs short; pes semidigitigrade to digitigrade; digits 3-3. Suborder 4. =Homalodontotheria=: teeth brachydont; lower molars similar to those of Toxodontia; limbs moderately elongate; pes semidigitigrade; digits with large curved claws, 5-5. Suborder 5. =Astrapotheria=: teeth brachydont to moderately hypsodont; canines enlarged into tushes; molars similar to those of Toxodontia; limbs greatly elongated; feet unknown. PROBOSCIDEA Order II. (see page 68) Suborder 1. =Pyrotheria=: incisors developed into tushes; molars bilophodont; limbs short, especially the lower element; feet digitigrade. LITOPTERNA This order of South American ungulates is less abundantly represented in the Deseado formation than in the Santa Cruz, but most of the genera of this latter formation have representatives in the Deseado so that they seem to have diverged still earlier. By Scott the order is divided into two families, the _Proterotheriidae_ and the _Macrauchenidae_, the less known Adiantidae being placed under the latter family until better known. I feel that I should prefer to retain the Adiantidae for the present, until they can be shown to be subordinate to another family, so that in this paper the three families are retained. The striking features of the two larger families may be best brought out by a comparison of their chief features as follows. Proterotheriidae Macrauchenidae 1 0 4 3 3 1 4 3 Formula --------- ------- 2 0 4 3 3 1 4 3 Upper inc. 2 and lower inc. Incisors, canine, and premolar 3 enlarged and tush-like, 1 simple, compressed, subequal growing from persistent pulps. in size, and rooted. Nasals normal. Nasals shortened indicating a proboscis. Neck short. Neck long. Feet with median digit enlarged, Feet with all three digits lateral digits reduced. subequal in size. =Proterotheriidae= Ameghino