

HISTORY OF WHALES 



57 



neck of the root is a well marked cingu- 

 lum. The root is gibbous below the neck. 

 Some of the teeth have the extremity of 

 the root irregularly divided into three 

 branches. The smaller teeth resemble the 

 anterior teeth of the living South Ameri- 

 can genus Inia in the shape of the crown, 

 the cingulum, and the compression of the 

 distally expanded root. None of these 

 teeth exhibit the distinct internal proto- 

 cone shelf that is so characteristic of the 

 crown of posterior teeth oilnia. 



In 1 891, Burmeister described and fig- 

 ured an imperfect skull collected by 

 Artemio Carreras at La Curtiembre, near 

 Parana,, Argentine Republic. In restoring 

 this skull, Burmeister used the living 

 Stenodelphis as a model and added the end 

 of the rostrum of another porpoise. This 

 composite specimen was erroneously re- 

 ferred to Saurodelphis argentinus, as has 

 already been pointed out by Abel (1909) 

 and Rovereto (191 5). Burmeister was the 

 first to suspect that this extinct porpoise 

 might be identical with Ischyrorhynchus 

 vanbenedeni, but it remained for Cabrera 

 (192.6) to allocate the skull to that genus 

 and species. This strongly telescoped 

 Lower Pliocene porpoise skull differs from 

 all known iniid skulls in having the 

 zygomatic processes placed far forward, 

 and the maxillaries are pushed farther 

 back toward the occiput. The outer 

 borders of the maxillaries in the supra- 

 orbital and supratemporal regions are 

 strongly bent upward, recalling Platanista 

 in some respects. Doubtless a certain 

 resemblance exists between Ischyrorhynchus, 

 Inia, and Platanista, but not a close one. 

 It is obvious that the lateral crests of the 

 maxillaries were much higher than in 

 Inia, and it is possible that when complete 

 they may have resembled those of Plata- 

 nista. The inclination of the posterior 

 wall of the narial passages is much less 

 steep than in either Inia or Platanista, 



and the small, conspicuously elevated 

 vertex is formed by the frontals. Al- 

 though both nasal bones are missing, the 

 cavities in which they were lodged are 

 distinct enough to determine their pro- 

 portions, and it is fairly certain that they 

 were pressed against the frontals on the 

 posterior wall of the narial passages. 

 The irregularly spaced teeth are large, 

 elliptical in section; the crowns of the 

 teeth are conical and low, with apex 

 slightly recurved backward, and covered 

 with rugose enamel. The roots of the 

 teeth are thickened, and the anterior 

 teeth are strongly inclined forward. The 

 imperfect skull, which lacks the end of 

 the rostrum, has a length of about 2.5 

 inches and was nearly 13 inches in breadth 

 across the zygomatic processes when 

 complete, while a large complete skull 

 of Inia has a length of but 2.1 inches and a 

 zygomatic breadth of 9! inches. 



Skulls of living river porpoises of the 

 family Iniidae differ from all other odonto- 

 cetes in having a more or less fenestrated, 

 freely projecting, fortuituous process of 

 the maxillary, extending backward out- 

 side of the sinus in front of the choana to 

 or beyond the level of the sphenoid fissure. 

 The South American Bouto (Inia geoffrensis) 

 and the Chinese Peh Ch'i (Lipotes vexillifer), 

 now living in Tung Ting lake and its 

 tributaries, are porpoises of small or 

 moderate size whose skulls have elon- 

 gated rostra; narrow facial depression with 

 external borders of maxillaries bent up- 

 ward; maxillaries extending forward to 

 extremity of rostrum; orbits situated in 

 front of level of narial passages; nasals 

 flattened up against frontals on anterior 

 wall of braincase, contributing upper 

 border of posterior wall of narial passages 

 and overspread inferiorly by mesethmoid; 

 elevated vertex; elongated zygomatic 

 processes; palatine forming part of an- 

 terior wall of narial passage and separated 



