MORPHOLOGICAL REVISION OF THE SUBORDER. 87 



fonned by the reverted edge of the anterior articular face. This is the characteristic 

 feature upon which Cope founded T. retraversa. 



In the Ihird caudal the faces for the capitulum and tuberculum are as in the 

 second but a strong ridge runs backward from the posterior edge of the capitular face 

 on the side of the centrum ; this ridge occurs only on the single vertebra and may be 

 only an unimportant variation. 



^he. fourth to the seventh are similar to the preceding, the tubercular and capit- 

 ular faces are united, growing smaller. 



The eighth shows the capitular face almost completely reduced, the rib is small 

 and projects horizontally. 



The ninth has the rib reduced to a small process and the capitulum and tubercu- 

 lum are no longer distinguishable. 



There are no chevrons or intercentra preserved in the caudal series, nor are the 

 lower edges of the centra cut out for the intercentrum unless this begins to appear on 

 the last caudal. 



The shoulder girdle is not preserved. 



The anterior limbs are not preserved. 



t\\& pelvic girdle (plate 3, fig. 6) is nearly perfect; both sides are preserved. The 

 pelvis has been opened out on the ischio-pubic symphysis nearly flat, but the bones of 

 the two sides are hardly disturbed. The distal ends of the ischia and pubis are broken 

 away, but that is the only damage the pelvis has sustained. 



The ilium has a strong crest which is turned sharply to the rear a short distance 

 above the acetabulum ; this portion is relatively narrow vertically ; its inner face shows 

 a deep semilunar impression divided in its upper part by a sharp ridge for the attach- 

 ment of the sacral ribs. The ilium takes a large part in the acetabulum, sending 

 down a wide wedge-like portion that forms much of the cavity of the acetabulum and 

 divides the pubis and ischium except at the lower border of the acetabulum. 



The ischium has a heav}' end which forms a prominent postero-inferior edge for 

 the acetabulum. The distal portion extends far back and its upper edge, though not 

 thickened, is slightly incurved. The ischia of the two sides meet in a symphysis, but 

 the attachment was confined to the edges and did not extend to any considerable por- 

 tion of the inner side as in the Clepsydropidce where the sides of the pelvis were more 

 nearly vertical. The suture line between the ischium and pubis is distinct and their 

 point of contact on the symphysial edge is marked by a notch ; the opposition of the 

 notches of the two sides left a small cartilage-filled space. This may be a feature of 

 youth. 



"tXvt pubis takes a relatively small part in the acetabulum. Its distal portion forms 

 a prominent border which unites with that of the ischium so that the lower edge of the 

 acetabulum is marked by a prominent ridge. The upper edge of the distal portion is 

 thickened into a strong ridge which extended to the distal end. The obturator fora- 

 men lies just below the anterior edge of the acetabulum and runs almost directly 

 upward and inward. 



The posterior limbs are represented by the femora and tibia of both sides (plate 

 3, figs. 5, 7). The upper end of the femur is very wide so that the depression on the 

 posterior face is relatively much wider than in Dimetrodon; it ends sharply below. 

 The two sides of the cavity are marked by sharp ridges, but the radial process is rela- 

 tively small. From the lower end of the cavity a sharp ridge extends to the outer con- 

 dyle. This closely resembles the same ridge on the femur of Eryops, but starts anew 



