82 bulletin: museum of comparative zoology. 



From the anterior border of the spiracles to the presumed ex- 

 tremity of snout 11.5 in. (292 mm.) 



Breadth of skull above, across the occipital crests 5.0 in. ( 127 mm.) 



Breadth at base, between the temporal bones 6.5 in. (165 mm.) 



Longest diameter of largest tooth at the socket 0.35 in. (8.9 mm.) 



Besides the foregoing, we may poiut out the following important characters 

 whose combined weight is considered sufficient to establish beyond doubt the 

 Platanistid relations of the form in question. (1) The cervical vertebrae are all 

 free, and each one is of considerable length for a Cetacean; (2) the general form 

 of the skull resembles that of Inia and Pontoporia (= Stenodelphis), but is rela- 

 tively narrower behind, and has steeper lateral and posterior walls ; (3) the large 

 and nearly vertical parietals are widely separated from each other by the upward 

 crowding of the supraoccipital, which is also wedged in between the frontals at 

 the summit : in this region the frontals are visible only as narrow bands, contin- 

 uous with the tumid nasals in front, enclosing the interparietal between them, 

 and being themselves almost entirely concealed behind by the overroofing laminae 

 of the maxillary elements ; (4) the temporal fossa is large, and would appear to 

 have been open in front; that part of the squamosal supporting the zygomatic 

 process is very massive, and the orbital portion of the maxillary and frontal is 

 correspondingly thickened; (5) the pterygoids are displaced from contact with 

 each other in the median line through intervention of the vomer, and do 

 not enclose an involuted air-space open behind; they entirely surround the 

 palatines as in Inia and Pontoporia, and may have had (though this cannot be 

 determined definitely from the present condition of the specimen) an articulation 

 with the squamosal behind ; the basal portion of the rostrum is wide and trans- 

 versely arched ; and (6), the premaxillaries, of extremely dense structure, are 

 separated by a deep longitudinal cleft, and are broadly expanded without being 

 inflated on either side of the narial orifices. 



Prom the review already given it appears that, with the exception of Brandt 

 and Abel, authors are agreed in including Lophocetus among Platanistids, but 

 hold different opinions concerning which of the two subfamilies, Platauistinae or 

 Iniinae, it is more nearly related. With Cope, we are persuaded that there is 

 much greater structural resemblance to Inia and Pontoporia than to Platanista, 

 among recent forms. The highly characteristic maxillary crests of the susu are 

 not present in Lophocetus, the pterygoids do not unite in the median line to form 

 an arch which almost entirely conceals the palatines, the latter do not extend in 

 advance of the pterygoids along the basal portions of the rostrum, and the supra- 

 occipital joins the parietals along crests that rise vertically and then flare slightly 

 outwards, instead of being concave inwardly, as in the susu. On the other hand, 

 as compared with Inia, only unimportant differences are found. The walls of the 

 brain cavity are less rotund, the crests, as connoted by the generic name, are 

 more powerfully developed, the nasals are crowded backwards so as to override 

 the frontals at the vertex, which latter is divided by a deep longitudinal cleft, and 

 the premaxillaries are more widely separated. The occipital condyles are rela- 



