14 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 76 



Bones of both rostral and cranial portions of the skull departing con- 

 spicuously from their normal mammalian relationships ; braincase broad 

 and short; teeth increased above the normal eutherian number or 

 secondarily reduced or absent. 



Maxillary with orbital plate present; ascending process of maxillary 

 small and narrow, interlocked with body of frontal, not spreading 

 over the expanded supraorbital process ; braincase telescoped chiefly 

 from behind ; bones forming wall of narial passage always retaining 

 essentially normal relationships ; region of base of mesethmoid roofed 

 over by nasals and by median portion of f rontals ; teeth present in 

 large numbers in embryos but not known to occur in adults ; baleen 

 always present in adults [For key to families and genera see 



page 20] Mysticeti. 



Maxillary with orbital plate absent ; ascending process of maxillary 

 large and broad, not interlocked with body of frontal, spreading out- 

 ward over the expanded supraorbital process ; braincase not tele- 

 scoped chiefly from behind ; bones forming wall of narial passage 

 usually departing conspicuously from normal relationships ; region 

 of base of mesethmoid usually not roofed over by nasals or by 

 median portion of f rontals ; teeth normally present in adults; baleen 

 always absent [For key to families see page 33] Odontocf.ti. 



THE DETAILS OF TELESCOPING AND THEIR RELATION TO 

 CLASSIFICATION 



While telescoping in each of the suborders of modern cetacea has 

 followed a course which is very consistent as to its main features 

 the various genera are found to arrange themselves according to 

 stages and minor variations of the process. Each of these special 

 peculiarities of detail is well marked and constant for the genera in 

 which it occurs, a circumstance that would of itself indicate definite 

 importance in classification. This importance is, however, greatly in- 

 creased by the fact that with every stage or detail of telescoping 

 there is associated, in other parts of the skull and skeleton, a special 

 set of characters which are often so well marked that they would by 

 themselves be sufficient to define the same groups, but which do not 

 necessarily present in their degrees of development any parallelism 

 with the progress of telescoping. Conditions of this kind appear to 

 be most clearly expressed by according family rank to the various 

 groups and by arranging the groups primarily in accordance with 

 the progress of that essential process by which the excessively modi- 

 fied modern cetacean skull seems to have been developed from the 

 ordinary mammalian structure. The course of this advance appears 

 to have been influenced in each individual case by varying combina- 

 tions of the same two general tendencies which have been seen (p. 4) 

 to underlie the differentiation of the twO' main types of telescoping. 



