INIA GEOFFRENSIS AND PONTOPORIA 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 skull of Jnia a com- 
parison with this nearly allied form. 
The skull (Pl. XXVIII.) is that of a perfectly adult animal. The sutures are par- 
tially obliterated, and the bones are compact and heavy. Many of the teeth are broken, 
some having been lost during life and the alveoli filled up ; the remainder are considerably 
worn at the points. The rostrum is curved downwards towards the extremity, much 
more so than in the Paris specimen; this is probably the effect of age, as a similar 
change takes place in Jnia 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......00cs.ccencravccsesdsecccenaicesss senearannens 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 
[ISHS ctgandeseonne eee an aos oe ap aedaaonosAnaadedtaccrconnnn ye 13°5 
Greatest breadth (across zygomatic process of squamosals) 4°8 
Breadth of foramen Magnum ............sceeeneeeererencereee Heit 
Breadth of occipital condyles ..:.......:...:cesscssreeraeeoneee 2°4 
Breadth across antorbital processes of frontals............... 2°6 
Breadth of rostrum at base ...........sseceneeeeeeceeeeeeeenees 1:8 
Breadth of rostrum at middle ..........0..-.--seseeeeeenseenes 0-6 
Mandible, length ......2...002csesseaseadenseeseceneeecrescoeeres 13-7 
Mandible, length of symphysis ...........0.+.+sseeeeeeeeeeeeees 8-0 
Greatest breadth posteriorly ............eseeeeeeeeneeeeees waste yeeiieo 
Height at the coronoid process............:ssesseeeeeeeeeeeeees 2°3 
The supraoccipital is broader and shorter than in Jnia, 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 Jnéa 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 
