120 



MEMOIRS OF THE UNIVERSITY OF CALIFORNIA. 



The hum ems is in all cases a relatively slender element; though not greatly 

 elongated, it is not greatly expanded distally. The radius is extraordinarily 

 long and slender for an ichthyosaurian, and the median constriction is pro- 

 nounced. Between the epipodial elements is a gap as wide as that in the limb 

 of any typical shore reptile. The ulna is also relatively long and shows a me- 

 dian constriction. The posterior portion of this element begins, however, to 

 show the expansion so frequently occurring in aquatic types, and the posterior 

 notch has been almost closed. 



In specimen 9950 (pi. 11), as in several others, a transverse row of three 

 small discoidal elements is seen next the distal end of the epipodial segment. 

 These bones are almost circular in form, and they do not occupy the entire 

 transverse space opposite the epipodials, so that they were evidently implanted 

 in a heavy cartilaginous plate. In specimen 9148 a similar row of bones is 

 seen. Prom their occurrence in this position there can be little doubt that these 

 elements are carpals. 



Pelvic Arch. The elements of the pelvic arch (pi. 12, figs. 1-4) have been 

 found in nearly their natural position in several specimens. The broad plate- 

 like ventral elements were evidently united along the median line somewhat as 

 in Toretocnemus (fig. 69, p. 55). 



The ischium has much the same form as in 

 Delphinosaurus perrini but may in some cases 

 (pi. 12) show a shallow antero-internal notch 

 giving it a form approaching that of the pubis 

 of Delphinosatirus. Excepting the notch just 

 mentioned the form is also not unlike that of the 

 ischium in Mixosaurus. 



The pubis resembles this element in Toretoc- 

 nemus in that the proximal end is perforated by 

 a large obturator foramen. In the only speci- 

 mens which are perfectly preserved this opening- 

 Fig. 134. Cymbospondylus petrinus Leidy. j s completely closed by bone. The transition 



Ischium, specimen 9! '\. ^^ ^ ^ to ^ ^ ^ &,#,. 



would be made easily by breaking down the bar of bone between the obturator 

 foramen and the margin. 



The ilium has a considerably expanded proximal head with an elongated 

 and transversely expanded superior blade. The form resembles that of Del- 

 jiliii/o.murus, though distinguished from it by the wider expansion of the blade 

 and the absence of a posterior tubercle. Judging from its position in specimen 

 9950, the superior blade of the ilium was directed upward and forward to its 

 sacral attachment. 



Pelvic Limb. The posterior limb is represented by the femur in the most 



