INIA GEOFPEENSIS AND PONTOPOEIA BLAINVILLII. 107 



Inia was written, a second skull of Pontoporia, also from the mouth of the Rio de la 

 Plata, was received at the British Museum, as a present from Dr. Hermann Burmeister, 

 of Buenos Ayres. With his wonted liberality, Dr. Gray immediately informed me of 

 its arrival, and has permitted me to add to the description of the skuU of Inia a com- 

 parison with this nearly allied form. 



The skull (PI. XXVIII.) is that of a perfectly adult animal. The sutures are par- 

 tially obliterated, and the bones are compact and hea-^^. Many of the teeth are broken, 

 some having been lost during life and the alveoli filled up ; the remainder are considerably 

 worn at the pomts. The rostrum is curved downwards towards the extremity, much 

 more so than in the Paris specimen; this is probably the eifect of age, as a similar 

 change takes place in Inia and some other Dolphins. The mandible partakes also 

 of this curve. The small, rounded and. depressed cranium, and very long, narrow and 

 compressed beak, give a remarkable appearance to this skull, reminding one, as Gervais 

 remarks, of the head of a scolopacine bird. 



The principal dimensions are : — 



Extreme length 15-8 



Length of rostrum (from anterior end of premaxillary to 



bottom of antorbital notch of maxillary) 11'2 



From anterior end of premaxillary to lower edge of nasal 



bones 13'5 



Greatest breadth (across zygomatic process of squamosals) 4 '8 



Breadth of foramen magnum I'l 



Breadth of occipital condyles 2-4 



Breadth across antorbital processes of frontals 2-6 



Breadth of rostrum at base 1"8 



Breadth of rostrum at middle 0'6 



Mandible, length 13-7 



Mandible, length of symphysis 8-0 



Greatest breadth posteriorly 4-5 



Height at the coronoid process 2-3 



The supraoccipital is broader and shorter than in Inia, terminating in front by a much 

 more open angle, and on each side in a low ridge, coming in close contact with the broad 

 posterior extremities of the suprafrontal plates of the maxillaries. In the ankylosed 

 condition of the bones it is impossible to say whether any of the frontal intervenes 

 between them. The temporal fossa resembles that of Inia in its extent and form. 

 The zygomatic process of the squamosal is proportionally longer, and meets the post- 

 orbital process of the frontal. The relative forms of the parietal, squamosal, and frontal 

 bones, as they appear in the temporal fossa, more resemble those of Platanista than of 

 Inia; but a narrow piece of the parietal prevents the union of the frontal and squamosal 



