MIOCENE PORPOISES — KELLOGG 125 



Another vertebra (USNM 20659), which was associated with a section 

 of the rostrum, represents the second in the dorsal series. The posi- 

 tion of these vertebrae in tlie dorsal series here adopted is based on the 

 structural features of the dorsal vertebrae of Inia geojffrensis as well 

 as on the articular relations of the ribs associated with this fossil. 

 All of these vertebrae have the epiphyses firmly ankylosed to the 

 centrum, indicating that the porpoise was fully matm-e. 



These vertebrae may be distinguished from the corresponding 

 vertebrae of Inia geqffrensis by the wider interval separating opposite 

 prezygapophysial facets, the larger neural canal, and the location 

 of the articular facet for the capitulum of the corresponding rib 

 on the centrum at the upper posteroexternal angle. They differ 

 also from the corresponding vertebrae of Eurhinodel'phis in that the 

 pedicles of the neural arches and the prezygapophyses are more 

 noticeably robust, the neural canals are narrower, and the anterior 

 surfaces of the centra are narrower. The centra increase in length 

 from the second to the tenth in the series. The width of the interval 

 separating the prezygapophysial facets decreases markedly from 

 the second to the tenth dorsal. These prezygapophysial facets 

 are rather large and slope steeply from outer to inner margins. On 

 four of these dorsals the diapophyses are relatively short, and the 

 facet for articulation with the tuberculum of the corresponding 

 rib, with the exception of the fourth dorsal, is situated behmd the 

 level of the anterior surface of the centrum. The facets for the 

 tuberculum of the corresponding ribs are noticeably elongated dorso- 

 ventrally on the second and fourth dorsals, but progressively widen 

 anteroposteriorly to the tenth dorsal. The postzygapophysial facets 

 do not differ markedly from one another on the fourth, sLxth, and 

 eighth dorsals. On each side of the centrum of the fourth and sixth 

 dorsals at the upper posteroexternal angle there is a large facet for 

 the accommodation of the capitulum of the following rib. This 

 facet, however, is not present on the eighth dorsal. On the cor- 

 responding vertebrae of Inia, however, these facets are located on 

 the upper anteroexternal angle of the centrum. 



Second dorsal: When this vertebra (USNM 20659) was found 

 the neural spine, the left half of the neural arch, and a portion of the 

 left side of the centrum had been broken off while exposed on the face 

 of the cliff. The centrima (pi. 11, fig. 3) is approximately the same 

 size as that of the second dorsal of Lophocetus calvertensis. This 

 second dorsal, however, differs from the corresponding dorsal of Inia 

 in having a wider neural canal, slightly longer diapophyses with the 

 dorsoventrally elongated facet for the tuberculum located obliquely 

 on the posterior half of the extremity of the latter, and widely sepa- 

 rated prezygapophysial facets, the distance between their outer margins 



