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SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 76 



second specimen), or in Van Beneden's drawing of the original type 

 skull. The absence of the plate, which seems to be real and not due 

 to mutilation of the fossils, is an indication that Patriocetus belongs 

 definitely among the toothed cetaceans ; as it is probable that in any 

 form actually preceding the modern baleen whales the plate would 

 necessarily be present, and its size would with little doubt be relatively 

 greater than in existing members of the group. 



PhyseteridcB. — The family Physeteridcc is not definitely known to 

 be represented by more than two genera, the living Physeter and the 

 Miocene "" Paracetiis " of Cope. Its characters consist primarily of a 

 combination of telescoping-type, development of the facial depres- 

 sion, structure of the zygomatic arch, palatine and pterygoid, and 

 the relation of the posterior ribs to the vertebrae ; features which are 

 not commonly preserved in fossils, but without a knowledge of which 

 no positive classification of a cetacean genus is possible. The pala- 

 tine bone retains its horizontal position in the roof of the mouth. 

 It is overridden from behind by the pterygoid ; but the general rela- 

 tionships of the two bones to the neighboring cranial elements is 

 otherwise so normal that the conditions present in Physeter can 

 readily be explained as the result of simple telescoping of elements 

 originally in about the same relative positions as those in ordinary 

 carnivores. While the narial passage shows a distinct trace of the 

 primitive backward slant it is situated mostly behind the level of the 

 orbit. There is no longitudinal median ridge on the forehead behind 

 the narial aperture. The posterior orifice of the infraorbital canal 

 is formed by the maxillary and lacrimal, the relationship of these two 

 bones, so far as the orifice of the canal is concerned, being not very 

 dififerent from that which exists in the fox (pi. 3, figs. 4 and 5). 

 Atlas distinct, the other cervical vertebrae fused with each other and 

 with the first dorsal, a combination of relationships unknown in the 

 cervicals of any other cetacean. Among the insufficiently known 

 extinct cetaceans the genus Thalassocetits appears to be the one which 

 is most probably a member of the physeterine group. Its frontal and 

 maxillary are figured as not widely unlike those of Physeter, but the 

 remains are very fragmentary. The possibility that Diaphorocctus 

 {" Hypocetits") may belong in the same group must also be con- 

 sidered. On the other hand Physetcrula is more likely to be a del- 

 phinid with the orbital edge of the frontal thickened in a manner that 

 is unusual though not unknown among the dolphins ; and the 

 Physodon patagonicus of Lydekker, as described and figured, can 

 with equal probability be referred to the Delpliinidce. In this animal 



