In many ways, the family suggests Nesodontidae, and undoubtedly belongs to that series, if not directly ancestral. The lower molars are distinctly of the same type as in all the other toxodonts, but show a tendency to become hyposodont.
The following genera have been assigned by Ameghino to the family. Some of them are based on very scant material and I have ventured to suggest in each case what disposition I have felt to be the proper one.
Leontinia, the type genus, is described in detail on [pages 109-115].
Scaphops is based on a mandibular symphysis, which is wider than usual for Leontinia, and on a second upper incisor which is compressed. The species in the genus Leontinia show a marked degree of variability, and I can see in this only individual variability, so that I place Scaphops under Leontinia and S. grypus, as a synonym of L. gaudryi.
Steniogenium is based on a mandibular symphysis with roots only of the teeth. The incisors are proclivous and inc. 3 small. I consider this also as Leontinia, and the species S. sclerops as a synonym of L. oxyrhynca, which I think is the female of L. gaudryi.
Ancylocoelus is a valid genus, differentiated by its dental formula
- 3 0 4 3
- ———,
- 3 0 3 3
the loss of the upper canine and the lower canine and first premolar distinguishing it from either Leontinia or Colpodon.
Rodiotherium is based on a mandibular symphysis which would indicate an animal with the same formula as the foregoing genus, differing only in that lower incisor 3 is large. This, to my mind, does not make a generic character, and at most the species, R. armatum, can only be considered an independent species belonging to the genus Ancylocoelus.
Loxocoelus is a very questionable genus, based simply on an upper molar, which “is similar to that of Homalodontotherium, but more squared.” I feel that in regard to this genus it should stand as unknown until more material is found.