SYSTEMATIC REVISION OF THE SUBORDER. 75 



Table V. — Contrasting the Characters of the Different Species of the Genus Dimetrodon — Cont'd. 



D. incisivus. 



1. Spines laterally flattened at bottom, changing to rounded above; finely striate. 



2. Third to sixth cervical vertebra; with the axis through the neural spine and the middle of the centrum 



nearly vertical. 



3. Intercentrum small in the mid-dorsal and lumbar regions ; without capitular facets at the end. 



4. Lumbars with distinct keel. 



5. Size medium. From 1.6 to 2 meters. 



D. doHovianus. 



1. Spines square at base, rounded above ; smooth. 



2. Third to sixth cervical vertebras with the axis through the neural spine and the middle of the centrum 



inclined strongly forward. 



3. Intercentra in the mid-dorsal and lumbar regions small and without terminal facets for the capitulum of 



the ribs. 



4. Lumbars with low, sharp keel on the mid-line of centrum below, this keel divided by a shallow, longitu- 



dinal groove. 



5. Size that of D. incisivus. 2 to 2.6 meters. 



D. macrosfondylus. 



1. Spines rectangular, oblong below, changing to rounded above ; not striate, smooth. 



2. Third to sixth cervical vertebras with the axis through the neural spine and the middle of the centrum 



vertical. 



3. Intercentra of the mid-dorsal and lumbar regions larger and with the ends enlarged to carry a facet for the 



capitulum of the rib. 



4. Mid-line of the lumbars with a sharp longitudinal keel. 



5. Size smaller. 1.2 to 1.6 meters. 



D. ^latycentrus. 



1. Spines similar to those of D. 7nacrosfondylus. 



2. Third to sixth cervical vertebrae with the axis through the neural spine and the middle of the centrum 



vertical. 



3. Intercentra as D. macrosfondylus. 



4. Mid-line of the lower surface of the centra of the lumbar vertebrae not keeled, but broad, flattened, and 



rather rugose. 



5. Size almost that of D. macrospoyidylus. 



D. ohtusidens. 



1. Spines as in D. macrospondylus, but with very prominent and slender fore and aft ridges at the base. 



2. Third to the sixth cervical vertebrae with the axis through the neural spine and the middle of the centrum 



vertical. 



3. Intercentra of the mid-dorsal and lumbar regions small and without terminal facets for the capitulum of 



the rib. 



4. Lumbars with keel on the mid-line of centrum below. 



5. Size, small, i to 1.3 meters. 



D. natfajot'icus. 



Most of the characters given above not recognizable. Size small, i to 1.3 meters. 



Humerus with entepicondyle proportionately very much longer than in any other species of the genus. The 

 radial crest is separated from the proximal end by a considerable space. 



D. longiramus. 

 New species indicated by the slender proportions of the jaw and small articular face for the head of the 

 humerus in the scapula. 



Table VI. — Contrasting the Characters of the Species of the Genus Naosaurus. 



N. cruciger. 

 Spines with the cross pieces above the first pair reduced to tuberosities. 



N. clavigcr. 

 Spines heavy and clumsy, with cross pieces commonly double and relatively long even to the apex of the spine. 



N. Tnicrodus. 

 Spines slender and elegant, cross pieces relatively long even to the apex of the spine. 



