CETOTHERES FROM THE MIOCENE CHOPTANK FORMATION 



31 



tenuated neural spine (pi. 18, fig. 9) rises 85 mm. above 

 the roof of the neural canal. Both prezj-gapophysial 

 facets are incomplete internally but were obviously 

 elongated and extended forward beyond the level of 

 the anterior face of the centrum. A narrow half -moon- 

 shaped articular surface on the anterior border of the 

 lateral face of the centrum represents an enlargement 

 of the capitular facet on the posteroexternal angle of 

 the centrum of the first dorsal. The large deep capitular 

 facet on the posteroexternal angle of the centrum for 

 reception of the capitulum of the third rib is similar in 

 shape and size to the corresponding facet on the first 

 dorsal. The median longitudinal ridge is broad; the 

 ventral and lateral surfaces of tlie centrum resemble 

 closely the fii-st dorsal. The anterior and posterior faces 

 of the centrum are transversely widened and broadly 

 subcordate. 



Third dorsal. — The transverse processes (dia- 

 pophyses) are slightly broader, shorter and directed less 

 forward than those of the second dorsal, expanded at 

 the extremity to provide a large facet (length, 47 mm.; 

 vertical diameter, 28 mm., greatest on anterior half of 

 its length and also attenuated posteriorly), and are 

 extended forward noticeably beyond the level of the 

 anterior face of the centrum. The thickened basal por- 

 tion of this diapophysis (pi. 20, fig. 3) arises from the 

 transversely widened pedicle of the neural arch (right, 

 minimum width, 41 mm.) and the dorsoexternal portion 

 of the centrum anteriorly. The pedicle of the neural arch 

 is robust and rather short. Prezygapophysial and post- 

 zygapophysial facets are largely destroyed. Neural spine 

 is (pi. 18, fig. 10) wider than that of the second dorsal, 

 and rises 99 mm. above the roof of the neural canal. 

 Anterior face of the centrum is transversely widnened 

 but more subcordate in outline. A more crest-like median 

 ventral longitudinal ridge separates shallower de- 

 pressed ventral and lateral surfaces. A large postero- 

 external facet for capitulum of the fourth rib and a 

 reduced narrow demifacet on the anteroexternal border 

 adjacent to the capitular facet on the second dorsal are 

 present. 



Fourth dorsal. — A slight increase in the length (65.5 

 mm.) of the centrum as well as in the height (110 mm.) 

 of the neural spine (pi. 18, fig. 11) above the roof of 

 the neural canal characterizes this vertebra. Tlie robust 

 transverse jirocesses (diapophyses) do not differ materi- 

 ally from those of the third dorsal, each being projected 

 outward, but less extended forward beyond the level 

 of the anterior face of the centrum. The extremity of 

 each diapophysis (pi. 20, fig. 4) is expanded to provide 

 a large concave pitted facet (length, 50 mm.; vertical 

 diameter, 31 mm., greatest on anterior half of its length 



and attenuated posteriorly) for the tuberculum of the 

 fourth rib. The main axis of this facet is almost hori- 

 zontal. The broad basal portion of each diapophysis 

 arises from the transversely widened pedicle of the 

 neural arch (right, minimum width, 40 mm.) and from 

 the dorsoexternal portion of the centrum anteriorly. 

 The prezygapophysial facets are almost flat and are 

 located on the low, bluntly pointed metapophyses. A gap 

 of 90 mm. separates the prezygapophysial facets ante- 

 riorly. The postzygapophysial facets are elongated, 

 rather broad and slope obliquely from internal to exter- 

 nal margins. The neural spine is materially broader at 

 the base than that of the third dorsal and more nar- 

 rowed distally; it rises 110 mm. above the roof of the 

 neural canal. The subcordate anterior face of the cen- 

 trum is transversely widened but flattened dorsally. A 

 narrow median ventral longitudinal ridge separates the 

 concavely excavated ventral and lateral surfaces of the 

 centrum. A large protuberant posteroexternal facet for 

 the capitulum of the fifth rib and a much narrower demi- 

 facet on the anteroexternal border adjacent to the 

 capitular facet on the third dorsal are well developed. 



Fifth dorsal. — The fifth dorsal is characterized by 

 rather widely separated prezygapophysial facets (95 

 mm. anteriorly), which are elongated (40 ±: mm.) and 

 shallowly concave. The robust transvei-se processes 

 (diapophyses) are essentiallj' similar to those of the 

 fourth and each projects forward beyond the level of 

 the anterior face of the centrum. The rugose facet 

 (length, 48 mm.; vertical diameter anteriorly, 29 mm.) 

 for the tuberculum of the fifth rib on the expanded 

 extremity of each diapophysis is concavelj' excavated 

 in a horizontal direction and slopes downward and in- 

 ward from the dorsal to ventral margins. As on the 

 fourth dorsad, the broad basal portion of each diapoph- 

 ysis arises from the transversely widened pedicle of 

 the neutral arch (right, minimum width, 35 mm.) and 

 from the dorsoexternal portion of the centrum anterior- 

 ly. The low bluntly pointed metapophyses project 

 noticeably beyond the level of the anterior face of the 

 centrum. The elongated postzygapophysial facets are 

 very narrow and project backward beyond the level of 

 the posterior face of the centrum. The width of the 

 neural spine (pi. 18, fig. 12) has increased. The contour 

 of tiie anterior face of the centiiun (pi. 20, fig. 5) does 

 not differ materially from that of the fourth dorsal, but 

 the median ventral longitudinal ridge is less prominent 

 although it separates the deeply excavated lateral sur- 

 faces of the centrum. The posteroexternal facet for the 

 capitulum of the sixth rib is as strongly protuberant as 

 on the preceding dorsal, although the anteroexternal 

 demifacet is barelv discernible. 



