AKT. 28 SKULL OF ZAKHACHIS FLAGELLATOR KELLOGG 5 



and their posterior margins form a continuous curve with the pos- 

 terior border of the protuberance behind the nasal passages. There 

 is a relatively large dorso-ventrally compressed foramen in the max- 

 illa at the posterior extremity of the premaxilla which opens into a 

 short, deep groove. 



In the preceding paper it was stated that "skulls of Lipotes and 

 Inia may appear more specialized than that of Zarhachis "^ because 

 of the elevation of the vertex and the shifting of the nasals to a 

 vertical position." This opinion was based upon a small fragment 

 of bone which appeared to represent a portion of the vertex. Fur- 

 ther on ^ it was said that " this fragment is very important, for it 

 shows tliat the vertex of the skull was not strongly elevated, or at 

 least no prominent protuberance, like in Inia or Lipotes, was pres- 

 ent." On reexamination it has been found that this fragment differs 

 in a number of respects from the vertex of the second skull. The pro- 

 tuberance behind the nasal passages may have changed with age and 

 varied according to sex. Nevertheless certain peculiarities of this 

 fragment are not readily interpreted on the basis of conditions in the 

 second skull, and there are some features which suggest the inter- 

 pretation given in the preceding paper. This second skull, however, 

 shows that other portions of the attempted restoration are incorrect 

 and also that the protuberance behind the nasal passages is broader 

 than in Inia and Lipotes. 



The nasal bones do not overhang the nasal passages ; their antero- 

 posterior diameter is about equivalent to one-half of their breadth. 

 The nasals are applied to the anterior surfaces of the frontals, as in 

 Lipotes and Inia, but they are proportionately larger bones and 

 actually increase the size of the protuberance behind the nasal pas- 

 sages. From a dorsal view the nasals are almost subtriangular in 

 outline, but the posterior margin is more or less emarginate and the 

 anterior concave. Inferiorly they are overepread by the extremities 

 of the ectethmoids. In the case of Inia and Lipotes the nasals con- 

 sist of thin plates of bone applied to the anterior surface of the pro- 

 tuberance behind the nasal passages, and their doreal margins do 

 not extend upward to the level of the dorsal surfaces of the frontals. 



A narrow interparietal may be present between the crest of the 

 supraoccipital and the protuberance behind the nasal passages. A 

 narrow groove follows the posterior border of this protuberance, and 

 may possibly represent a suture between the combined frontals and 

 the narrow strip of bone which, because of its position, may very well 

 represent the interparietal. An interparietal seems to be present in 

 the skull of Inia geofrensis (Cat. No. 239667, U.SN.M.). Both con- 

 dyles are visible when the skull is viewed from above. 



* Kellogg, R., Proc. U. S. Nat. Mus., vol. 63, 1924, p. 7. 



• Kellogg, R., Idem, p. 13. 



