the last upper molar is the smallest, in place of the largest of the whole series of teeth. [Illustration: FIG. 74.—The penultimate and last right lower molars of _Halitherium fossile_; from the Miocene of the Continent. (After De Blainville.)] _Other forms._—Remains from the Pliocene of France described as _Prohalicore_ are regarded as indicating a Sirenian closely allied to _Halicore_; while a molar from the Tertiary of California has been made the type of _Desmotylus_, which is likewise referred to the _Halicoridæ_. _Dioplotherium_, from the Phosphorites of South Carolina, has been considered to connect _Halicore_ with _Halitherium_, but even its ordinal position is uncertain. A portion of a skull found in the Pliocene of Belgium has been described as _Crassitherium_ by Van Beneden; and some compressed teeth, somewhat similar to but larger than those of the Dugong, discovered in the Miocene of the department of Lot-et-Garonne, France, gave origin to the genus _Rytiodus_ of E. Lartet. Of this genus, which may be identical with _Trachytherium_ of the French Miocene, better preserved remains have subsequently been described by Delfortrie. These show that the rostrum is more elongated than in _Halitherium_, but the skull is otherwise very similar, as are the molar teeth. The incisors are very large, exserted, strongly compressed, almost sabre-like, rounded on the upper or anterior surface, sharp below, concave on the external and convex on the inner side, and transversely striated.