40 SMITHSONIAN' MISCELLANEOUS COLLECTIONS VOL. 72 



grow to a disproportionate size and to a high degree affect the form 

 of the jaw. 



The Tertiary European Xiphirostrum {" Ziphirostrum," " Miosi- 

 phius"), which is known from parts of the skull, has in a single 

 respect gone further than Mcsoplodon, near to which it otherwise 

 stands : the intermaxillaries have grown over the mesethmoid and 

 come in contact with each other along their upper margins. But 

 Xiphirostrum. must have taken its origin from whales that were less 

 far advanced than the known species of Mesoplodon; as the mes- 

 ethmoid is not ossified anteriorly ; the teeth in the upper jaw are 

 slightly less atrophied, leaving traces behind them in the maxillary ; 

 and at the front of the lower jaw there are two well-developed teeth 

 on each side. 



Chonoxiphius {" Choneziphius ") , likewise Tertiary European and 

 known from parts of the skull, stands near to Xiphirostrum. It has 

 gone further in the modification of the face. The facial cushion has 

 begun to modify a special area around the nares for its bed. Here 

 the lateral margins of the premaxillaries are caused to grow slightly 

 upward, so that they together, and the bones that lie between, form 

 a special pit, a structure the first traits of which, more or less evident, 

 are found in many other toothed cetaceans. In the middle of the pit 

 there has arisen an erect longitudinal crest, evidently formed from 

 the posterior part of the mesethmoid. (The under jaw is probably 

 not known.) 



Xiphius {"Ziphiiis") appears to have originated from whales 

 which stood on about the same level as Mesoplodon. Its deviations 

 are of two principal kinds : ( i ) the median part of the occipital wall 

 is forced further back and raised higher upward, so that the nasal 

 bones, which are even more modified than in other Xiphiines and are 

 widened out plate-wise in front, once more come to form a forward- 

 bent roof over the nasal cavity, and (2) the lateral margins of the 

 intermaxillaries have grown upward as in Chonoxiphius, but much 

 more conspicuously, bounding a deep pit. As in Mesoplodon the 

 anterior part of the mesethmoid becomes ossified with age. 



In the genera of the group Hyperoodontes, which must have 

 originated from the lowest Xiphii, the bony crest, a faint indication 

 of which is found in many toothed cetaceans running along the upper 

 surface of the maxillary in front of and over the orbit, becomes so 

 stimulated to growth by resistance of the water that it gradually 

 swells up to a huge hump which spreads itself over most of the face 

 in front of the nares. Each hump is closely appressed to its fellow 



