NO. 5 TELESCOPING OF THE CETACEAN SKULL 5 1 



tions present in the iniids, and perhaps representing a structure more 

 primitive than that now existing in the true dolphins. Posterior orifice 

 to the infraorhital canal formed by the maxillary alone. Teeth of 

 normal delphinine type, with no tendency toward a tusk-like manner 

 of growth. Cervical vertebrse retaining their primitive condition of 

 separateness. The living genus Stcnodclphis, with its extinct rela- 

 tives, appears to represent a well defined group best treated as a sub- 

 family of the Dclphiiiidcc. The structure of the pterygoid and +he 

 absence of a backwardly projecting maxillary plate at the side of the 

 palate distinguish it sharply from the Iiiiidcc and connect it with the 

 Dclphinid(c through morphological features similar to those present 

 in the otherwise very different Dclphinaptcrus. Its even more funda- 

 mental imlikeness to Platanisfa is shown by the strictly delphinine 

 type of telescoping and of pterygoid structure, as well as by the large 

 size of the palatine and the absence of other modifications connected 

 with extreme backward-forcing of the base of the beak. 



Dclphinapfcrincc. — A similarly isolated position as regards the ordi- 

 nary dolphins is occupied by the genus Dclphinapterus which shares 

 some of the peculiarities of Monodon and some of those of Stenodcl- 

 pJiis. In contrast with Monodon, however, the ])osterior basal 

 portion of the pterygoid is spread laterally over the alisphenoid, and 

 in most skulls there is an evident outer pterygoid reduplication like 

 that present in S ten odd phis; though the teeth are tusk-like in manner 

 of growth the general character of the dentition is normal, with 

 several functional teeth of approximately equal size in each jaw ; 

 some of the hindermost teeth, especially in the upper jaw, show a 

 distinct trace of a tricuspid crown structure when unworn (See True, 

 Smithsonian Misc. Coll. Vol. 52, p. 329, April 28, 1909, and Lonnberg, 

 Arkiv. for Zoologi, Vol. 7, pp. 2-4, fig. i, July 5, 1910.). The cervical 

 vertebrae, as in both Monodon and Sfenodclphis, retain their primitive 

 condition of distinctness, and the orbits are situated at a level in front 

 of that occupied by the nasal passages. These characters, es])ecially 

 those of the teeth, have led Lonnberg to regard the genus as the 

 representative of a distinct family. They appear, however, to be of 

 no more than subfamily value. 



Monodoniincc. — The genus Monodon has usuall\- been associated 

 with Delphinapterus, principally because in these two genera the 

 cervical vertebrae differ from those of most other living dolphins in 

 retaining their primitive separateness. Similarity between the two 

 genera is also shown by the manner of growth of the teeth, by the 

 conspicuous participation of the palatine in the formation of the 



