ART. 26 REMAINS OF FOSSIL PORPOISES KELLOGG 27 



terior dorsals the basal portions of the neural arches extend prac- 

 tically the entire length of the centrum, but in the ninth dorsal as 

 well as in the more posterior ones they have receded from the 

 posterior epiphyses. As will be noted from an examination of the 

 figures, the backward projecting mesial portion of the neural arch 

 becomes progressively shorter toward the posterior end of the series. 

 The principal differences to be noted between this dorsal and the 

 anterior ones are the length of the neural spine, the length of the 

 centrum, the position and length of the diapophysis, and the close 

 approximation of the postzygapophysial facets. 



On account of the contact between the diapophysis and the para- 

 pophysis it appears probable that this vertebra (pi. 9, fig. 3) is the 

 ninth dorsal. At least it is the last one in the dorsal series that 

 retains a diapophysis. The most apparent differences between this 

 vertebra and the preceding are the more noticeable constriction of 

 the mesial portion of the centrum, the increase in length of the 

 neural spine, and the narrowness of the neural canal. On the first 

 two or three dorsals the diapophyses arise high up on the neural arch 

 and when followed backward along the series they are seen to grad- 

 ually shift their position until on the ninth dorsal they project from 

 the base of the arch. In the third dorsal the distance from the in- 

 side margin of the neural arch to the tip of the diapophysis is 46.5 

 mm. The same measurement for the ninth dorsal is 18.5 mm. 



On each side of the centrum of the third, fifth, and sixth dorsals, 

 below the level of the neural arches and in front of the posterior 

 epiphysis, there is a circular depression for the accommodation of 

 the capitulum of the following rib. On the seventh dorsal there is a 

 corresponding articular surface behind the anterior epiphysis and 

 below the base of the neural arch. 



The tenth dorsal (pi. 7, fig. 9) is characterized by a short bread 

 parapophysis, high and narrow neural canal, long neural arch, and 

 the small size of the postzygapophysial facets. The prezygapo- 

 physial facets of the third, fifth, and sixth dorsals are more'nearly 

 horizontal in position than are those of the ninth, tenth, and eleventh. 

 The metapophyses project beyond the epiphj-ses in all of these 

 dorsals, but the postzygapophyses do not. The anterior margin of 

 the parapophysis on the tenth dorsal (pi. 9, fig. 2) is nearer to the 

 anterior epiphysis than is the posterior margin with the other 

 epiphysis, while in case of the eleventh dorsal (pi. 9, fig. 1) both 

 margins near the base are almost equally distant from their 

 corresponding epiphyses. Furthermore, the parapophyses of the 

 eleventh dorsal tend to incline backward. On these last mentioned 

 dorsals, the articular facets for the tubercula of the ribs are elongate 

 and shallowly concave. These vertebrae differ among themselves in 



