ABT. 14. MARYLAND FOSSIL PORPOISE — KEIJ:,OGG. 15 



with the zygomatic process of the squamosal and is closely appressed 

 to that bone. The postorbital projection is exceedingly long in Inia 

 and slightly shorter in Lipotes^ but does not extend backward to the 

 zygoma in either of these genera. On skulls of Inia and Lipotes, the 

 lachrymal is closely appressed to the anterior face of the supraorbital 

 process. The lachrymal and ankylosed jugal are missing on the left 

 side of this fossil skull. Originally the lachrymal must have been 

 inserted between the overlapping maxilla and the anterior face of the 

 supraorbital process, as will be shown in another part of this de- 

 scription. 



The zygomatic process of the squamosal is greatly thickened dorso- 

 ventrally in contrast to the long attenuate zygoma of Inia and 

 Lipotes. As a whole the zygoma is robust, curved, and rather short; 

 the dorsal surface curves gradually forward and upward. The 

 posterior margin of zygoma is nearly straight and forms an obtuse 

 angle with the axis of the rostrum. Correlated with this difference 

 is the form of the glenoid cavity and the postglenoid process. The 

 latter is relatively thin, directed backward and downward. The 

 greatest length of the zygomatic process along the glenoid face is 

 99 mm. and the greatest depth is 63 mm. On the whole the zygoma 

 bears a much closer resemblance to Eoplatanista italica Dal Piaz ® 

 than to any living river dolphin. 



Ventral view. — The ventral surface of the rostrum (pi. 1) is 

 formed almost entirely by the maxillae which meet mesally in a 

 linear suture in front of the vomer, and extending forward parallel 

 each other throughout the distal three-fourths of the rostrum. All 

 of the teeth in either tooth row are lodged entirely in the maxillae. 

 The maxillae broaden from the tip of the rostrum to the maxillary 

 notches. The rostrum is not narrowed between the tooth rows and 

 the maxillary notches as in Lipotes. The lateral borders of the max- 

 illae establish the margins of the rostrum and posterior to the tooth 

 rows these margins are thin and bladelike. The rostrum is eniar- 

 ginate at the tip, the sides of the notch being formed by the pre- 

 maxillae, small splintlike processes of which extend forward be- 

 yond the maxillae. On either side the premaxillae are not visible 

 from a ventfal view posterior to the first tooth. Posteriorly, as re- 

 marked above, the maxillae separate to allow the keel of the vomer 

 to appear between them. This keel of the vomer is continued back- 

 ward, and increasing in height, attains its maximum depth at nasal 

 passages and then abruptly subsides. 



Posteriorly the maxillae are overlain by the external pterygoids. 

 Near the proximal end and in a middle line each maxilla comes in 



« Dal Piaz, G., Gli odontoceti del Miocene Belluiiese. Parte Quarta. Eoplatanista 

 Italica. Memorie dell'Istituto Gcclogica delJa R. Universita di Padova, vol. 5, pi. 1, 

 tig. 1, 1916. 



