﻿TCHTTIYODORULITES. 



125 



1860. Haplacanthus tenuisulcatus, E. von Eichwald, Leth. Rossica, 

 vol. i. p. 1599, pi. lvii. fig. 19. 



The type species. 



Form, fy Log. Devonian : near St. Petersburg. 



P. 2252. Fragment of spine. Egerton Coll. 



Genus HETER ACANTHUS, Newberry. 



[Palseoz. Pishes N. America (Mon. U. S. Geol. Surv. no. xvi. 

 1889), p. 65.] 



Spines small or of moderate size, much laterally compressed, broad 

 and triangular, and gently arched ; internal cavity very large, 

 opening by a long fissure at the convex border ; base of insertion 

 short or absent. Sides of exserted portion ornamented with broad, 

 flattened, smooth, longitudinal ridges, bifurcating and intercalated 

 towards the base ; the ridges having finely crenulated margins, 

 separated by very narrow, fissure-like sulci. 



Keter acanthus politus, Newberry. 



1889. Heteracanthus politus, J. S. Newberry, torn. cit. p. 66, pi. xxi. 

 figs. 4, 5. 



Type. Columbia College, New York. 

 The type species, not represented in the Collection. 

 Form. 6f Log. Hamilton Group (Upper Devonian) : Milwaukee, 

 Wisconsin. 



Heteracanthus heterogyrus (Agassiz). 



[Plate III. fig. 6.] 



1845. Onchus heterogyrus, L. Agassiz, Poiss. Foss. V. G. R. p. 117, 

 pi. xxxiii. figs. 16-18. 



Type. Unknown. 



This species is assigned to Heteraeanihus on account of the 

 characters of the superficial ornamentation. Both the type specimen 

 and the example recorded below appear to be fragmentary, thus not 

 exhibiting the original form of the spine. 



Form. &f Log. Devonian : N.W. Russia. 



P. 2248. Fragment of spine, partly shown, of twice the natural 

 size, in PI. III. fig. 6. The ornament is precisely similar 

 to that of the type species, which the writer has examined 

 at Columbia College. Egerton Coll. 



