

HISTORY OF WHALES 



55 



marine formation at Darwin Station, 

 Santa Cruz Territory, Argentine Republic, 

 is in many respects quite specialized. The 

 relationships of Proinia are somewhat 

 doubtful, for the structures needed for 

 definite classification, such as the ar- 

 rangement of the bones below the choanae 

 and the maxillaries, are missing. Cabrera 

 (19x6) has recently suggested that these 

 remains belong either to Diochotichus or 

 to a closely related genus. It is obvious 

 that it is much larger and quite distinct 

 from either Inia or Litotes. As compared 

 with Inia, it is less specialized in having 

 a larger exposure of the frontals on the 

 vertex, more nearly vertical and less for- 

 ward sloping narial passages, and supra- 

 orbital processes with less elevated 

 extremities. The skull of Proinia presents 

 the following characters: abruptly ele- 

 vated vertex formed by large rectangular 

 median portions of frontals, narrow supra- 

 orbital processes of frontals directed 

 obliquely forward, orbit anteriorly 

 situated, large temporal fossae bounded 

 above by strong ridges or crests, outer 

 wall of braincase convex, and zygomatic 

 process convex externally with well de- 

 veloped postglenoid process. Granting 

 that Proinia is a true iniid we must look 

 further back in geological time for the 

 progenitors of this family, for contempo- 

 raneous squalodonts were highly special- 

 ized and well established in the early 

 Miocene. Abel, Winge, Miller, and 

 others have construed the available data 

 as showing that the iniids, if not closely 

 related, at least lean toward the 

 squalodonts. 



A section nearly 8 inches in length of 

 the symphysial region of the mandibles, 

 with six pairs of alveoli and without 

 longitudinal external furrow, which was 

 found associated with four loose teeth in 

 the upper San Pablo formation near Rodeo, 

 California, formed the basis for Hespero- 



cetus californicus (True, 1912.). This late 

 Upper Miocene porpoise has been referred 

 to the Iniidae chiefly on account of the 

 conformation of the symphysis and the 

 shape of the teeth. The teeth have 

 slightly recurved crowns covered with 

 rugose enamel in addition to a longitudi- 

 nal postero-internal carina and an antero- 

 external carina. The teeth are further 

 characterized by the lack of a distinct 

 cingulum, the absence of an enlarged 

 protocone shelf, and the imperceptible 

 constriction of the root below the crown. 

 They are separated by wide interspaces, 

 those of the upper jaw fitting in between 

 those of the lower jaw and vice versa 

 when the jaws are shut, and their apices 

 rest in the interalveolar depressions. 



Another extinct porpoise, Saurodelphis 

 argentinus, with iniid affinities occurs in 

 the Lower Pliocene Parana formation of 

 the Argentine Republic. The original 

 material, consisting of two fragments of 

 a mandible collected by Montes de Oca 

 on the shore of the Parana River, was 

 described and figured by Burmeister in 

 1871. Subsequently (1891), Burmeister 

 erroneously referred an incomplete skull 

 of Ischyrorhynchus vanbenedeni to Saurodel- 

 phis argentinus, and as a result of this 

 mistaken allocation the affinities of this 

 fossil porpoise were misinterpreted for 

 many years. The larger fragment of the 

 type specimen, which consists of a portion 

 of the symphysis with 6 teeth and 6 empty 

 alveoli on the left side, and 3 teeth and 4 

 empty alveoli on the right, is 15 inches 

 long, and its greatest height is 2.. 5 inches. 

 A distinct furrow, beginning at the pos- 

 terior end of the symphysis and extending 

 forward to near the extremity, traverses 

 the lower border of the external face. 

 The alveoli are elliptical, and behind and 

 anterior to each is a small circular de- 

 pression placed outside of the alveoli 

 instead of in line with them, apparently 



