54 



PERMO-CARBONIFEROUS VERTEBRATES FROM NEW MEXICO. 



rather deep spout leading into the narrow and deep concavity formed by the ischia. 

 The perfect condition of the two pubes of specimen No. 651 permits an accurate 

 coaptation of the whole pelvis, an upper view of which is shown in fig. 32 b. The 

 true pelvis, it is seen, is narrow, the greatest diameter of its brim being scarcely 

 more than an inch, and its depth is less than 2 inches. And this is the outlet 

 through which the eggs of a creature nearly 6 feet in length must have passed. 

 The obturator foramen pierces the pubis in its usual place. Between the pubes 

 and the ischia, as articulated, there is a diamond-shaped pubo-ischiadic vacuity 

 of moderate size, as in all the true pelycosaurs. 



The ischium (fig. 32) is of the usual shape, an elongated, hatchet-shaped bone 

 meeting its mate in an acute angle below. Its upper posterior border is thickened and 

 everted, and there is an angular excision between it and its articulated mate behind. 



What the significance of the peculiarly elongated and horizontal expansion of 

 the pubes is we can not suggest ; that it has something to do with the habits of the 



Fig. 33. Ophiacodon mirus Marsh, X K- A, left femur, ventral surface; B, left femur, fibular side; C, right 

 femur, ventral side; D, right femur, dorsal side; E, right femur, tibial side; F, left fibula, ventral side; 

 G, left fibula, tibial side. 



animal seems probable. In the present genus the massive symphysis between the 

 pubes indicates a firm and strong pelvis, one able to sustain a considerable weight. 

 In Limnoscelis the massive symphysis extends through both pubes and ischia; in 

 Seymonria the pubic symphysis is weak, while that of the ischia is deep; in both 

 Dimetrodon and Varanosaurus the symphyses of both ischia and pubes are slight. 

 Femur: The femur is relatively stout, its extremities considerably expanded. 

 The digital fossa extends a full third of the length. The trochanter stands out 

 prominently, but ends abruptly, not continuing into the adductor ridge. Below 

 the trochanter, on the fibular side, there is a distinct roughening for the attach- 

 ment of muscles. The tibial condyle projects strongly inward from the longitudinal 

 axis of the bone, its articular surface looking inward at an angle of about 45 degrees. 

 As usual, the fibular condyle has much the larger articular surface, which is con- 

 nected by a narrow band on the ventral side with that for the tibia. Neither 

 surface can be seen broadly from the dorsal side, indicating a normally much flexed 

 knee in life. The left femur (fig. ^^ a) has a remarkable anomaly: On its fibular 

 side (fig. 33 b) the proximal articular surface is broad and has a distinct rim separat- 

 ing it by a considerable interval from an elongate oval cartilaginous surface at the 



