292 



forms an ellipsoidal longitudinal convexity, with the lower half more 

 prominent and appearing to be an articular eminence. The outer extremity 

 of the spine is broken, but it appears to have been rounded transversely, 

 though it may have been pointed. 



The measurements of the spine are as follows: 



Inches. 



Lengtli of the spiue iu its present couclitiou IG 



Lines. 



Breadth of the spiue beyond the articular hook 17 



Breadth at the iuuer third 21 



Breadth at tlie middle 23 



Breadth uear the distal eud 20 



Thickness of the spine beyond the articular hook 14 



Thickness at- the inner third 9J 



Thickness at the middle - 6 



Thickness near the distal end 3 



The transverse section of the spine near the middle forms an irregular 



ellipse, as represented in the accompanying 

 figure. The left-hand side beneath represents 

 the posterior groove opening downward. 



Since writing the above,* I have had the op- 

 portunity of examining the proximal half of a similar spine, from L'Eau 

 qui Court County, Nebraska. It was found in association with remains of 

 Mosasaiirus, &c., by George S. Truman, and presented by him to Swarth- 

 more College, Pennsylvania. 



aANOIDEI. 

 PYCNODUS. 



This genus, typical of an extinct family of fishes, was originally indicated 

 by Agassiz in the Poissons Fossiles. Many species have been described, 

 mainly from teeth and fragments of jaws with teeth, which are comparatively 

 large and stout, and were adapted to crushing hard food, such as mollusks 

 with their shells, crustaceans, &c. The remains have been found in the Tri- 

 assic, Jurassic, Cretaceous, and early Tertiary formations of Europe. 



Pycnodus faba. 



A specimen, represented in Fig. 16, Plate XIX, indicates a species to 

 which the above name has been given. It was submitted to my examination 

 by Dr. William Spillman, who obtained it from the Cretaceous formation near 

 Columbus, Mississippi. ' . 



