A DESCRIPTION OF THE GENUS DIMETRODON, COPE. 



47 



articular faces are nearly round. The transverse processes curve outwards and downwards 

 as in the axis, but the distal end peaches much further ventrally and is below the neuro- 

 central suture for about a centimeter. The spine rises vertically from the centrum to a 

 height of .147 m. It is broad and stout at the base, but suddenly contracts a short dis- 

 tance above it and ends in a, slender rod curved slightly forwards. Between the 

 bases of the preezygapophyses and the spine depressions exist, which become deep elon- 

 gated pits in the dorsals. 



Now follows a, gap of two vertebrae. The sixth has a cylindrical body and round 

 articular faces. The lower edges of the faces are extended ventrally, forming a slight 

 flange or apron, which becomes very prominent in the posterior dorsals. The middle 

 portion of the anterior edges on each side are reflected, forming an articular face. The 

 transverse processes are short and stout, and .stand out directly from the body of the 

 neural arch. The articular face looks outwards and slightly backwards. From the ante- 

 rior edge of the face a, narrow process, bearing an articular face, runs down to the face on 

 the anterior edge of the centrum. This shows that in the cervical region the capitulum 

 and tuberculum of the ribs wen; still united. 



The transverse process stands well above the centrum. There is a, deep excavation 

 at its base, running back to the notch between the posterior zygapophyses and the posterior 

 edge of the centrum. This is interrupted near its middle by a ridge running up to the 

 posterior edge of the transverse process. Superiorly the transverse process joins imme- 

 diately the preezygapophyses, which are interrupted by a, deep notch near their base. The 

 articular faces of the postzygapophyses look outwards and down wards and meet on a small 

 keel below. The faces of the praezygapophyses look inwards and upwards, and are slightly 

 cupped. 



The spine is thin at the base and somewhat elongate antero-posteriorly, with a thin, 

 prominent ridge running up the anterior and posterior edges. A few centimeters above 

 its origin the spine becomes rounded and then flattened antero-posteriorly. The ridges of 

 the lower part disappear on the rounded part and are replaced by shallow grooves above. 

 The spine has already reached a great height, The part preserved measures .385 m. in 

 height, but this is only one-half of the spine. 



The seventh and the eighth cervicals (PI. II, Figs. 21, 22) differ only in degree from 

 the sixth, the transverse processes become more slender and the face connecting the 

 tubercular and the capitular faces nearly disappears. The pits above and below the 

 transverse process become deeper and the body of the centrum is more compressed. 



The first (?) dorsal is marked by a, total disappearance of the capitular face on the 

 anterior edge of the centrum. The centrum is a little higher and longer than broad. 

 The ends of the chorda 1 canal have broad funnel-like openings with flaring edges; the 



