Merriam.] 



Triassic IcMh yopterygia . 



7!) 



what is considered as the pubis in pacifism (PI. 14, fig. 2), a 

 small articular surface seems to lie present just below the hook, 

 and on this the ischium may have been received. 



This arch, as it is supposed to have been constructed, would 

 bear a greater resemblance to that of the Plesiosauria than to 

 any known relative of the Ichthyosanrs. It is so different from 

 that of Ichthyosaurus that no doubt can exist as to this genus 

 representing a separate line of descent. The arch of the known 

 Jurassic forms could hardly be derived from it. 



To the pubis of perrini the supposed coracoid of pacificus 

 (PI. 14, fig. 2), the type of the genus, shows a stronger resem- 

 blance than it does to any bone of the pectoral girdle, and inas- 

 much as it was associated with posterior dorsal vertebra?, it may 

 be considered as representing that element. Particularly in the 

 form of the proximal end it differs from both coracoid and scap- 

 ula and resembles the pubis (text Fig. 1 , p. 103) . In this connec- 

 tion it may be noted that the writer's association of the posterior 

 dorsal vertebra? with the supposed coracoid, as doubtful anterior 

 dorsals, was not without reason. His first opinion regarding the 

 vertebra? was that they were anterior caudals, but the evidence 

 in favor of their belonging with the undisturbed supposed 

 coracoids was so strong that he accepted as a possibility the 

 occurrence of a single articulation of the rib low down on the 

 centrum. This belief was strengthened by the discovery of long 

 single-headed ribs. 



Extremities. — The anterior limt>s are best represented in the 

 specimen of osmonti (PI. 10, fig. 1, and PI. 11). With 

 this there were found the right humerus, radius, ulna, radiale, 

 and a fifth bone that may be an intermedium; and from the 

 left side the humerus, radius, radiale, and a phalanx. The 

 elements that are considered as belonging to the right limb were 

 found together and in their natural positions iu a small slab at 

 the foot of the bluff. Close to them was what is known by 

 comparison with alexandrw to be the right scapula. The prox- 

 imal end of the right coracoid was exposed in the face of the 

 cliff near by. The left coracoid was buried in the limestone 

 just below the right, and the left humerus lay with its proximal 

 extremity next that of the coracoid. 



