[903-] 



Hay, North American Cretaceous Fishes. 



13 



front border of the fin is above, and the upper (bas.) rests on 

 one of the paired baseosts. 



No. 2009 of this Museum furnishes both cleithra of 

 ProtosphyrcBna perniciosa, which may be conveniently de- 

 scribed here. One of these is represented by Fig. 7. It is 

 possible that a small part of the bone is missing from the 

 upper end of the element. Compared with a specimen of 

 Tarpon atlanticus, 5 feet 6 inches long (1.67 m.), the cleithrum 

 is narrower. The portion below the curve is of the same 

 length, but the upper end of that of ProtosphyrcBna is about 

 50 mm. shorter. How much of this deficiency is due to in- 

 jury cannot be determined. The outside of the cleithrum 

 presents no features worthy of mention ; the surface probably 



Fig. 6. ProtosphyrcBna sp. 

 No. 1646. X 3. bas.^ baseosts; 

 cor.^ coracoid ; pct.^ pectoral fin ; 

 JC, scapula. 



No. 7. Protosphyrcena perniciosa (S^Ofe.). No. 2009. X 3. 

 Cleithrum seen from inner surface. 



has been convex in cross-section. On the inside we see, near 

 the upper border of the lower, or anterior, end, a deep groove 

 which is bounded both above and below by a sharp ridge. 

 On the hinder border of the upper, or posterior, portion there 

 is another groove. This appears to have started at the upper 

 end of the bone and to have run downward as far as the 

 articulation of the fin. It is possible that, as in Tarpon, some 

 accessory bone fitted in this groove. 



It is remarkable that, although this is perhaps the com- 

 monest species of ProtosphyrcBna, except perhaps P. nitida, 

 it is represented by remains of fins and shoulder girdle bones 

 alone. None of these have been found in association with 

 remains of the head. It appears to be possible that P. tenuis 

 Loomis and P. perniciosa are identical. The fins appear to 

 differ only in the character of the anterior edge, the angle 



