82 NEW YORK STATE MUSEUM 



Genus hetebacanthus Newberry 

 Gamphacanthus Miller 



Spines of moderate size, broad and laterally compressed at the base, 

 but soon becoming subtriangular in section, nearly rectilinear, and gradually 

 tapering toward the acute apex. Internal cavity relatively large, extending 

 nearly to the apex, and open on the posterior margin for a considerable 

 distance. No anterior keel ; posterior denticles not observed. Exserted 

 portion ornamented with finely crenulated longitudinal ridges which become 

 smooth and flat with wear, and are separated by fine, denticulate, intercostal 

 grooves. 



Heteracanthus politus Newberry 



1889 Heteracanthus politus /. S. Newberry. U. S. Geol. Sur. Monogr. 

 16: 66, pi. 21, fig. 4, 5 



1892 Gamphacanthus politus S. A. Miller. North Am. Geol. & Pal. p. 7 15 



1898 Heteracanthus politus C. R. Eastman. Am. Nat. 32: 552 



1899 Heteracanthus politus C. R. Eastman. Jour. Geol. 7 : 282 



Spines attaining a total length of about 20 cm, very broad at the base, 

 and with Ctenacanthuslike ornamentation. The longitudinal ridges, which 

 are rather numerous and closely apposed, become perfectly smooth when 

 worn, their presence being indicated only by the fine and deep intercostal 

 grooves — the so called "sinuous or denticulate longitudinal sutures" of 

 Newberry. More or less variation in size and number of the costae is to 

 be observed amongst different examples. The basal portion seems to be 

 regularly expanded, without forming an asymmetrical "shoulder" as in 

 Physonemus, Stethacanthus etc. 



Bilaterally symmetrical as these spines undoubtedly are, their position 

 must have been in the median line of the body, and not, as suggested by 

 Newberry and others, along the anterior margin of the pectoral fins. That 

 they belonged to Chimaeroids seems very probable, and they are an invari- 

 able accompaniment of the large dental plates described as Ptyctodus 

 ferox in the western Devonic. A characteristic Mesodevonic species, 

 it is interesting to note its presence in the fauna of the Portage shale, as 



