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University of California. 



[Vol. 3. 



helps to explain the occurrence of a similar constriction in the 

 more specialized humerus of Shastasaurus . A prominent ridge 

 on the upper side of the proximal end is opposite a much larger 

 elevation corresponding to the pectoral ridge on the inferior side. 

 Both prominences extend to about the middle length of the 

 humerus. A narrow ridge on the posterior distal angle of the 

 upper side is opposite a similar elevation on the ulna. The 

 radial and ulnar borders are both sharply concave as in Ichthyo- 

 saurus. 



The radius has exactly one- half the length of the humerus. 

 The anterior border is nearly straight, showing only a faint 

 indentation near the middle. The posterior border is deeply 

 concave. The surface of contact with the radiale takes up nearly 

 the whole of the distal end. The contact with the intermedium 

 is only along the posterior angle. 



The ulna has a deeply concave anterior border, and as in 

 Mixosanrus shows no emargination on the posterior side. The 

 facets for the intermedium and the ulnare are of nearly the same 

 length. A low triangular ridge is present near the posterior 

 proximal angle. 



The carpus and metacarpus consist of three linear series of 

 three bones each. The radiale is a little wider proximally than 

 the ulnare, and in consequence the intermedium articulates 

 principally with the ulna. The intermedium and the other two 

 ossicles of the middle linear series have entire margins. All the 

 elements of the two outer series are notched on the margins next 

 the lateral borders of the limb. In both right and left limbs the 

 metacarpal of digit one is deeply notched on both sides. 



The phalangeal region consists of three well developed digits 

 and the merest vestige of a fourth. There are seven phalanges 

 in digits one and three, and eight in the middle finger. The 

 terminal phalanges are exceedingly small and simple and it is not 

 probable that more than one or two have been lost from this 

 specimen. 



What may be considered as a rudimentary or perhaps as an 

 incipient digit four is represented in both right and left limbs by 

 two very small ossicles. These elements are opposite the first 

 phalanx in one limb and opposite the first and second in the 



