86 PALEOZOIC FISHES OF NORTH AMERICA. 
latter is eight inches. M. Van Beneden considered his specimen as generic- 
ally identical with a fish earlier described by M. de Koninck and himself,’ 
and which was made the type of a genus called by them Paladaphus ; but 
in my notice of Heliodus I pointed out that the two fishes differed in this, 
that while in Paledaphus the teeth were separated, forming a pair like those 
of Ctenodus, Dipterus, and Ceratodus, in Heliodus they are united to form a 
single symmetrical, rounded, or semicircular triturating organ. 
In an excellent article on Dipterus, Palcedaphus, ete., published by Dr. 
R. H. Traquair,” the opinion is advanced that the two species of Paledaphus 
(P. insignis and P. devoniensis) should not be separated, and that the genus 
Heliodus can not stand. From this opinion, however, I am compelled to 
dissent, and to maintain the integrity of Heliodus as a genus distinct from 
all its associates in the family of the Ctenododipterini (Dipterus, Ctenodus, 
Ceratodus, and Paledaphus insignis), for the reasons given in my description 
of the genus in the Paleontology of Ohio, viz: In all the genera enumerated 
the teeth consist of a pair of triturating plates in each jaw, the lower pair 
seated on the splenial bones, the upper on the palato-pterygoids. In Helio- 
dus, on the contrary, the dental apparatus of the upper jaw (we know 
nothing yet of the lower) consisted of a single dental plate, which represents 
the two teeth of the other genera united in one solid piece. This seems to 
me to be a character which has generic value. The specimen upon which 
my description is based remains unique, and is in the cabinet of the School 
of Mines, Columbia College. 
Hetiopus Lesteyr, Newb. 
Plate XVIII, Fig. 3. 
Heliodus Lesleyi N.; Paleontology of Ohio, voi. 2, p. 64, pl. 58, fig. 18. 
Upper dental plate rounded or hippocrepiform, one and a half inches 
in length and breadth; triturating surface more than a half circle, highest 
in the center, where it forms a broad smooth boss; from this radiate eight 
tuberculated ridges, four on either side of the median line, which is marked 
by a deep and smooth furrow. The ridges on each side differ among them- 
‘Bull. Royal Academy Belgium, 2d series, vol. 17, p. 143. 
2 Annals and Magazine Nat. Hist., July, 1878. 
