Mebbiam.] 



Triassic Ichthyopterygia . 



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the diapophyses separate from the upper articular surface, 

 the bases of the pedicels show little, if any, lateral extension. 



The lower arches begin at about the forty-fifth centrum. 

 Possibly they were present anterior to this point, but no traces 

 of them could be discovered. Articular surfaces for the chevrons 

 are seen as far back as the sixty-fifth centrum. No indications 

 of their existence are found beyond the bend in the tail. 



The ribs in perrini do not have the peculiar modification of 

 the head found in altispinus strongly marked. The articular 

 surface shows a little of the outward and backward curvature 

 seen in that species, but it is not so pronounced. In the dorsal 

 region the whole proximal end of the rib is sharply twisted, so 

 that its long diameter is moved almost eighty degrees from that 

 of the middle of the shaft. In this twist the lower portion of 

 the head and the flattened superior surface of the shaft are 

 directed forward. The anterior side is deeply furrowed by a 

 groove which begins on the upper side near the head, and may 

 extend about two-thirds the length of the shaft. The posterior 

 side is similarly channelled for about the same distance. The 

 distal end of the shaft is always nearly circular in cross-section. 



In the posterior portion of the dorsal region the ribs have 

 broad heads, but the shafts are short and apparently without 

 grooving. 



Excepting the fragment probably representing the shoulder 

 girdle, the limb and arch elements present have been described 

 in detail in the general discussion of the genus. 



The fragment resting upon the anterior dorsal ribs is too 

 imperfect for satisfactory determination, but is probably the 

 distal end of a coracoid. Its transverse diameter and thickness 

 bear about the same relation to the dimensions of the anterior 

 dorsal vertebrae as in al examine . 



The following table of measurements gives the dimensions of 

 the more important parts of this skeleton. All measurements are 

 in millimeters. The letter a preceding a measurement indicates 

 that it is approximated on a slightly broken specimen. 



