20 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.63, 



3Ieasurements of the skull. 



mm. 



Total length (estimated) 1,195. 



Length of rostrum (maxillary notches to tip of beak) 1,000. 



Breadth of skull across zygomatic processes of squamosals 268. 



Height of skull (basisplienoid to vertex, estimated) 122. 



Height of rostrum at level of maxillary notches 80. 



Total length of maxilla (estimated) 1,125. 



Greatest breadth of right premaxilla in front of nares 42. 



Greatest breadth of left premaxilla at maxillary notch 37. 5 



Breadth of rostrum at maxillary notches 155. 



Breadth of rostrum at proximal end of alveolar rows 98. 



Breadth of rostrum at extremity 25. 



Distance between inner margins of maxillae on vertex 28. 3 



Greatest breadth of left supraorbital process of the frontal 105. 



Greatest dorso-ventral depth of left supraorbital process of frontal 81. 



Greatest breadth of braincase between temporal fossae (estimated) 106. 



Length of exposed frontals on vertex 42. 



Breadth of exposed frontals on vertex 23. 



Length of right zygoma_^ 100. 



PERIOTIC. 



In general appearance the periotic of this fossil porpoise agrees 

 more closely with Platmiista gangetica (Cat. No. 23456, U. S. Nat. 

 Mus.) than with Inia geojfrensis (Cat. No. 49582, U. S. Nat. Mus.) 

 It is not distinguished from that of Platanista by any sharply 

 marked features other than the possession of a larger fenestra ovalis, 

 a more elongated internal acoustic meatus, and a wider interval be- 

 tween the foramen singulare and the cerebral orifice of the facial 

 canal. 



The posterior process is missing as the periotic is broken just pos- 

 terior to the fenestra ovalis. In case of some of the living dolphins 

 the posterior process is frequently damaged when an attempt is made 

 to remove the periotic bone from the skull and the destruction of the 

 back of the cranium maj^ account for the loss of the posterior proc- 

 ess of the periotic of this fossil porpoise. The internal and central 

 portion of the periotic represents the pars cochlearis. As a whole, 

 this structure is obliquely compressed dorso-ventrally and is less 

 convex than that of either Platanista or Inia; the posterior portion is 

 slightly elevated. The fenestra rotundum is large, and internally 

 a thin partition of bone separates it from the scala vestihnU. A 

 crescentic fissure following the course of the scala vestihvli is present 

 on the internal margin of this partition and this also corresponds 

 in its position to that of Platanista. In this periotic the fenestra 

 rotundum is more or less ovoidal in outline, but in a second specimen 

 the orifice is distinctly circular. The posterior face of the pars 

 cochlearis is rather abruptly truncated above the fenestra rotundum. 



