VEBTEBEATES. 253 



few relatively strong, sharp-crested, vertical ridges, which descend to 

 the basal line, though generally obsolete in the lower half of the face, 

 with similar, though perhaps less strongly marked costiein the posterior 

 face; when the surfaces are not abraded a dense enamel-like layer 

 occurs, which in the posterior face distinctly defines the basal limit of 

 the crown. Lateral diameter of base one to two-tenths inch, or about 

 twice the hight of the teeth. 



The affinities of the teeth described above are so intimate with Gla- 

 dodus as strongly to suggest their identity with that genus. Yet we 

 cannot mistake the characteristics which pertain to the form in question 

 and by which it is distinguished from the typical forms of the latter 

 genus. The coronal region even more strongly suggests relationship 

 with Phceoodus and Pristicladodus, as remarked in its entire definition 

 from the basal region, forming indeed an elevated ridge from which 

 arise the Cladodus-]ik& cusps, in a manner very similar to that observed 

 in the above mentioned genera. But in the basal characters we find a 

 marked divergence from the latter genera, and an equally striking like- 

 ness to that of Gladodus, with, however, this distinction, in the present 

 teeth the anterior basal border is uniform, without a break such as pro- 

 duced by median excavation or prominence. 



Their occurrence with the previously described form, Phcebodus Sophia;, 

 with which they bear intimate resemblauce in size, has raised the ques- 

 tion as to their relations with these teeth. Of course, it is possible they 

 represent the dentition of opposite jaws, in which case there would be 

 even a less marked dissimilarity than obtains respectively in the teeth 

 of the upper and lower jaws of some of the modern sharks, as instanced 

 in Scymnus. But, while we have no further evidence of such being the 

 fact, the unmistakable characters upon which their distinctive features 

 are based can scarcely be reconciled with a diversity of which we have 

 no analogy in the allied genus Gladodus. 



These, with the preceding described teeth, are among the earliest 

 pakeontological acquisitions of one of the writers, and it is with no inade- 

 quate sense of his deep obligations for the early traiuing and subsequent 

 friendship, that the present form is respectfully dedicated to Mr. Pat- 

 rick McIsaac, of Iowa. 



Position and locality : Magnesian limestone of the middle Devonian ; 

 Waterloo, Iowa. 



Genus PKISTIOLADODUS, McCoy, (amended.) 



The genus Garcharopsis of Agassiz, (Poiss. Foss. Ill, p. 313, G. prototypus, 

 carb. limest., Yorkshire and Armagb,) was founded upon imperfectly 

 preserved teeth, which probably are more intimately allied to the form 

 described by McCoy under the name Pristicladodus dentatus than with 



