l6 SMITHSONIAN MISCELLANEOUS COLLECTIONS \^0L. 72 



Balsenidae. — The group Mystacoceti with the single known family 

 BalcEnidce includes whales that stand near to the Zeuglodonts ; but the 

 most primitive members of the group had already advanced a step 

 further than the Zeuglodonts. They presumably had the number of 

 cheekteeth raised above the typical. With that change there followed 

 others. The most primitive Mystacoceti must have already had the 

 nasal aperture pushed further back than in the Zeuglodonts. The 

 intermaxillary probably extended further back. The maxillary must 

 have been somewhat more broadened out posteriorly. The parietal 

 was slightly encroached upon, and the braincase was a little tele- 

 scoped. The spinous processes of the dorsal vertebrae presumably 

 slanted to a less degree in different directions. The joints at the 

 elbow and wrist must have almo'st wholly lost their primitive structure, 

 etc. Taken all in all, however, the most primitive Mystacoceti must 

 have been in general like the most primitive Zeuglodonts. 



Of the many forms which the group Mystacoceti must have in- 

 cluded no others are known than a little circle of highly developed 

 genera very specially modified in their own direction ; but in spite of 

 their remarkable development they have retained many primitive 

 features which are no longer found in the other, higher families. 

 This holds good especially in the structure of the face. Although the 

 narial aperture is drawn backward into proximity with the anterior 

 wall of the braincase the nasal bone is not wholly misshapen. It 

 retains part of its long, narrow form and it still roofs over the hind 

 part of the nasal cavity which may yet inclose very considerable 

 remnants of the ethmoid plates. The anterior part of the nasal cavity, 

 bounded by the intermaxillary, maxillary and vomer, is also relatively 

 primitive in structure, more open than usual, with less tendency to 

 closing together of the bones. And the maxillary, although it has 

 expanded backward, and shoved itself somewhat back both above and 

 beneath the frontal, has nevertheless not in any way covered the 

 frontal's broad supraorbital process. A distinct lacrimal is present, 

 but this is not unknown among higher cetacea. The zygomatic arch 

 has retained more of its primitive form and strength than elsewhere. 

 Two outer nasal apertures are still found; they are not mutually 

 vmited. The basal part of the occipital is also to a somewhat less 

 degree modified than in other recent cetacea, being less specialized to 

 accommodate larynx and gullet. 



That which more than anything else has left its impress on the 

 known Balaenids is their habit of not hunting after single large fish, 

 but of swimming with open mouth into shoals of small fish, crus- 



