148 CATALOG OF FOSSIL FISHES IN THE MUSEUM 



canthidae the small teeth at the angles of the jaws, and those on the 

 gill-bars, were not of the Dittodus form, but had 3, 4 or more cones of 

 about equal size. Some of these were of the form usually referred to 

 Phcebodus, although unquestionably Pleuracanth as shown by their 

 position in the mouth of a Pleuracanth. Then, too, there are species of 

 Dittodus on record that have more than the usual two large cones — for 

 instance, Dittodus duplicatus (Newberry and Worthen),^^ which has 

 sub-equal denticles; and there are two species, mentioned by Agassiz 

 in his Poissons Fossiles, one with four,^^ and the other with five^^ 

 denticles. 



From this it appears that teeth which could be referred to Phcebodus 

 occur associated with Dittodus in the dentition of one fish. And from 

 all the specimens in hand it appears that a progressive series may 



cV^f ^ 



Fig. 52. Dittodus grahaiii, n. sp. Cotypes. X about 4 



A and B, show a large median denticle. C and E, show minute denticles between 

 the median and lateral denticles. D, shows root with the ' 'button." 



be arranged, leading by insensible stages from the one genus to the 

 other. Most Phcebodus species, it would seem, can be merged in 

 the genus Dittodus. The name Phcebodus should therefore be retained 

 as a provisional genus only, for teeth of which there is not a sufficient 

 nimaber of specimens to prove their gradation into Dittodus. 



The species is named in honor of Prof. A. W. Grabau, Professor of 

 Paleontology in Columbia University, as a token of our admiration 

 for his tireless devotion to paleontology, as well as to commemorate 

 his valuable work on the geology and paleontology of Eighteen Mile 

 Creek. 



^ Geol. Survey Illinois, ii, PalEeontology, 6i , pi. iv, figs. 3, 3a, i? 

 * Dittodus minutus. — Poissons Fos., iii, pi. xxiib, fig. 7. 

 ^' Ibid., iii, p. 204. 



