500 On the Fossil Fishes of the Carboniferous Limestone Series of Great Britain. 
many others are several species of the genus Polyrhizodus. They are described by 
Messrs. Newberry and Worthen in the Second Volume of the “Geological Survey of 
Illinois,” published in 1866. The genus Polyrhizodus is somewhat restricted by the 
authors to teeth like the British species, P. elongatus, shortly to be described—that 
is, to examples having a much longer lateral than vertical axis, with the crown of 
the tooth transversely low, and the root divided into numerous short, robust 
radicles. In addition, a second genus, Dactylodus, is originated, which includes 
specimens having essentially the same characters as those ascribed to Polyrhizodus, 
except that the tooth is relatively longer vertically than laterally, the crown oval, 
and the rootlets fewer in number (generally four or six), longer, and more robust. 
A careful study of the numerous specimens from the mountain limestone of 
Armagh leads to the conviction that no arbitrary line of the kind indicated in 
the separation of these teeth into two genera can be maintained. The species 
described in the following pages appear to be based on good reliable grounds, and 
are types of considerable numbers of specimens in each case. Some have the 
elongated form of the Polyrhizodus type of Messrs. Newberry and Worthen, whilst 
others pertain equally to that of Dactylodus. The occurrence of intermediate forms, 
however, bridges over the two genera and unites them ; or, if such be not the case, 
it will be necessary to create other genera for the accommodation of each separate 
form. It is probable that Messrs. Newberry and Worthen may have foreseen this 
generic identity ; for in the fourth volume of “ Survey of Lllinois” (1870), after 
describing a new species of Polyrhizodus (P. truncatus), they remark :—“A compa 
rison with the species we have named P. inflexus and P. porosus (Vol. IL., pp. 48, 
49, pl. 11, figs. 8 and 9), will show that they should be placed in one generic group 
with that now under consideration. From those species it is distinguished by its 
outline, lower and broader than in P. inflewus, less low and broad than in P. porosus, 
and by a root more nearly obsolete than in either.” The Polyrhizodus inflecus here 
referred to is described as Dactylodus inflexus, whilst the P. porosus is described as a 
Polyrhizodus. 
Polyrhizodus radicans, Agass. 
(Pl. LX., figs. 7, 8.) 
Petalodus radicans— L. Agassiz, 1840. “Rech. sur les Poiss. Foss.,” Vol. III., p. 174 
and 384. 
% y C. G. Giebel, 1843. “Fauna der Vorwelt,” Vol. L., pt. 3, p. 345. 
ss H. G. Bronn, 1848. <‘‘Nomencl. Paleont.,” p. 949. 
Polyrhizodus magnus—F. M‘Coy, 1848. “Ann. and Mag. Nat. Hist.,” 2nd Ser., Vol. IT.,. 
p. 126. 
Petalodus radicans— H.G. Bronn, 1849. “Knumerator Paleont.,” p. 646. 
3 J. Morris, 1854. “Cat. Brit. Foss.,” p. 337. 
Polyrhizodus ,, 33 1854, ee top p. 340. 
», (magnus) - 1854. Se 5 535 p- 340. 
A *; F. J. Pictet, 1854, “Traité de Paléont.,” Vol. II., p. 271. 
(Petalodus radicans) 5 1854. , - x p. 271 
