8 PROCEEDIXGS OF THE NATIONAL, MUSEUM. tol. 63. 



crease or angle is most conspicuous when viewed from the ventral 

 side and is situated in front of or internal to the glenoid fossa. The 

 absence of this crease or angle is one of the generic distinctions for 

 Mega/ptera^ for in this genus the anterior margin of the squamosal 

 extends in an even curve from the zygomatic to the falciform process 

 of that bone. The curvature of the anterior margin of the squamosal 

 in the skull of Parietobalaena corresponds with that of Cetotherium 

 megalophysum and Metopocetus durinasus, and thus differs from all 

 living balaenopterine whales. In Parietobalaena the anterior mar- 

 gin of the squamosal, as seen from the ventral view, slopes obliquely 

 outward and backward to a point on a line with the anterior margin 

 of the periotic and then because of the zygomatic projection is 

 directed rather abruptly forward. The angle is situated externally 

 and not internally, as in Balaenoptera. The foramen ovale is sit- 

 uated in a V-shaped aperture formed between the diverging glenoid 

 and falciform processes of the squamosal and their union with the 

 external pterygoid. 



In ventral view the lateral projection of the squamosal forms the 

 anteriorly projecting zygomatic process and the downward projecting 

 postplenoid process; the antero-internal portion of the squamosal is 

 bifurcated, forming the falciform and glenoid processes of that bone 

 and thus contributing to the formation of the foramen ovale; the 

 postero-internal portion is deeply indented and serves to lodge the 

 periotic. The left zygomatic process as seen from the ventral view 

 is slender and tapers anteriorly. The glenoid surface of the squa- 

 mosal lies in approximately the same plane as the basioccipital ; the 

 anticular surface is rather wide and concave antero-posteriorly. A 

 broad and deep channel for the external auditory meatus, which 

 commences at the postero-internal margin of the squamosal, continues 

 its course outward by winding around the postplenoid process of 

 that bone. The apophysis of the periotic fills in the space between 

 the exoccipital and the posterior margin of the groove on the squamo- 

 sal for the external auditory meatus. 



Ventrally, the frontals are produced outward, as mentioned pre- 

 viously, to form the expanded supraorbital plates. The right supra- 

 orbital plate is so incomplete that description will necessarily be lim- 

 ited to the opposite plate. It should be noted that the preorbital 

 surface — that is, the surface in front of the obliquely directed crest 

 which forms the anterior wall of the optic canal — presents no features 

 which would prevent or indicate an overspreading of this surface by 

 the horizontal ventral plates of the maxilla}. 



MEASUREMENTS OF THE SKULL. ^^ 



tnm. 

 Greatest breadth of skull across supraorbital processes (as preserved)— 349 

 Greatest transverse diameter of left frontal (measured in a straight line 



from inner margin of fi-ontal to tip of postorbital projection) 213. 5 



Least antero-posterior diameter of supraorbital process of frontal 66. 5 



