MORPHOLOGICAL REVISION OF THE SUBORDER. 1 23 



Measurements. — No. 4006 American Museum. 



mm. mm. 



Length of fragment of humerus preserved Total length of pubo-ischiatic symphyses as 



(about J4) '3° ^ P^'f f^'^l ■ V ; "^'^ 



Width of proximal end 89 Total length of femur . 250 



Vertical diameter of acetabulum, right side ... 175 Transverse width of head 85 



Other specimens of this species are: No. 4024 Am. Mus.: Caudals, 

 vertebrge, and the lower end of the femur. No. 1327 Am. Mus.: An axis. 

 No. 4051 Am. Mus.: A femur, vertebrae, and fragments of spines. No. 4034 

 Am. Mus.: A few nearly perfect spines. No. 4050 Am. Mus.: A maxillary 

 and premaxillary. 



Dimetrodon giganhomogenes Case (see p. 47, plate 22). 



Characteristic specimens : No. 1 1 2 University of Chicago : The type. No. 4043 

 Am. Mus. Nat. Hist., Cope, coll.: A few vertebrae with fragments of spines and a femur. 



In the type the bones were covered by a thin scale, which was readily removed, 

 leaving them in most excellent condition and undistorted. They were undisturbed in 

 the ground, and numbered as collected, so that the relative position of the dorsals and 

 lumbars is certain. The first vertebra preserved is evidently the third of the series. 

 The atlas and axis are missing. 



The t/iird cervical canies a keel on the bottom line which joins the posterior 

 edge sharply. On the sides are two longitudinal ridges; the first starts from the 

 anterior edge of the centnun near the middle and rises backward to near the middle 

 of the centrum, where it disappears. This ridge does not appear on the third cervical 

 oi Dimetrodon gigas (No. looi University of Chicago), but its absence may be due to the 

 crushed condition of the specimen. The second ridge is formed by the continuation 

 of the inferior supporting ridge of the transverse process to the posterior edge of the 

 centrum. Small centrosphenes and centantra are' present on the upper edges of the 

 articular faces. The transverse process is rather more slender than in Dimetrodon 

 gigas and reaches nearly to the lower edge of the centrum. The base of the spine is 

 rather elliptical in form, and terminates in anterior and posterior edges. About one- 

 third up the length of the spine it becomes sharply rugose, and then suddenly contracts 

 to a nearly cylindrical form. The apex is swollen and marked by vertical rugosities 

 showing the attachment of a ligament. The processes on the intercentnun for the 

 head of the rib are well-developed and very prominent, with the articular faces looking 

 almost directly backward. 



Th^/ojcrth cervical vertebra greatly resembles the third, except that the transverse 

 processes run more nearly straight down, not inclined to rear. The ridge on the side 

 of the centrum passing backward from the anterior face has disappeared. There is the 

 same inclination of the antero-posterior axis as in the third cervical, so that the posterior 

 face is lower than the anterior. The spine is straight and has no rugosity at the tip. 



A median dorsal has the bottom line sharply contracted below the intercentrum 

 to a keel not over i mm. thick and nearly one-third the height of the centnun. The 

 bottom line is straight, but the ends are widely flared so that the sides are sharply 

 concave. The centantra are present, but much smaller than in the cervicals. On the 

 anterior face the opening of the notochordal funnel is surrounded by a slightly 

 elevated ridge. The lower half of the anterior face is developed into a saddle-shaped 

 articular surface for the intercentrum. The transverse processes rise from the neural 

 arch above the neural canal and curve straight out and down, the lower end reaching 

 nearly to the lower edge of the centrum. The section of the transverse process is 



