INIA GEOFFEENSIS AND PONTOPORIA BLAINVILLII. 



89 



As Inia has always been supposed to have certain affinities with Platanista, I 

 have in the following description compared the different bones with those of that sin- 

 gularly modified Cetacean on the one hand, and of several of the ordinary Belphinidm 

 on the other. Fortunately the Museum of the College of Surgeons contains a 

 skeleton of the Gangetic Dolphin of nearly corresponding age with the subject of 

 the present communication, and I have also had frequently to refer to Eschricht's 

 valuable memoir upon the species*. 



The leading features of the skull have already been made known by d'Orbigny and 

 Gervais ; but I am able to add some further details regarding its structure. 



A comparison of the two skulls at the British Museum sent by Mr. Bates, with the 

 present example, shows only such differences as might be expected from the greater 

 age of the former, such as a more marked development of the ridges and prominences 

 in proportion to the size of the brain-case. The postnarial prominence especially is 

 more elevated and angular in the older specimens. The teeth differ somewhat in 

 number, as will be mentioned further on. 



The principal dimensions of the three skulls are as follows : — 



Extreme length 



Length of rostrum (from anterior end of premaxillary to bottom 



of antorbital notch of maxillary) 



From anterior end of premaxillary to lower edge of nasal bones 

 From anterior end of premaxillary to hinder edge of palate . . . 

 Greatest breadth, across zygomatic processes of squamosals . . . 



Breadth of foramen magnum 



Breadth of the occipital condyles 



Breadth across antorbital processes of frontals 



Breadth of rostrum at base (bottom of antorbital notches of 



maxiUaries) 



Breadth of rostrum at middle 



Mandible, length 



Length of symphysis _ 



Greatest breadth across the posterior ends of the rami 



Height of ramus at coronoid process 



Collected by 



Mr. Bates. Mr. Bates. Mr. Bartlett. 



a. I 4. I 



20-7" 



13-5 

 16-7 

 15-7 

 9-4 

 1-4 

 3-2 

 6-1 



4-2 

 1-4 



18-2 

 9-8 

 8-7 

 3-9 



19-4" 



12-7 



15-7 



t 



8-1 

 1-2 

 30 

 5-3 



3-5 

 1-2 

 17-0 

 9-4 

 7-3 

 3-4 



16-7" 



11-0 

 13-6 

 12-6 

 7-0 

 1-3 

 2-9 

 4-5 



3-1 

 1-1 

 14-2 

 7-3 

 6-5 

 2-9 



The want of symmetry so prevalent in the skulls of Dolphins is but slightly marked. 

 It can, however, be detected in a slight twist to the right of the hinder part of the 

 narrow median space between the premaxillary bones, and in the greater elevation on 

 the same side of the postnarial prominence of the frontal bones. Both maxillary and 

 premaxillary bones extend backwards to an equal extent on the two sides. 



In the cranium of the young specimen which forms the subject of the present commu- 

 • " Om OangesdelpUnen," Trans. Boy. Dan. Acad. 1851. Translated in Ann. & Mag. Nat. Hist, for March 

 1852. + Broken. 



02 



