508 On the Fossil Fishes of the Carboniferous Limestone Series of Great Britain. 
The third species, Chomatodus linear’s, Ag., possesses characters which separate 
some of the figured types clearly from both the genera Helodus and Petalodus, 
though there is evidently more than one genus represented. It is probable that. 
the small somewhat circular and thin tooth (op. cit., Pl. 12, fig. 5) is a Petalodont, 
allied to the genus Antliodus, N. and W., whilst some of the figures have more than 
a passing resemblance to Ctenoptychius. The majority of the figures represent 
examples having an elongated, more or less straight, cutting edge ; surrounded or 
not by concentric folds or plicee ; a somewhat expanded anterior and posterior 
coronal margin, and a short bi-concave root. ‘These teeth pertain, in all essential 
respects, to a Petalodont type, very similar in form to the most elongated species 
of Polyrhizodus, except that the root or base is simple and undivided. Figs, 8, 
9, 10, 12, and 13, loc. cit. seem to represent teeth possessing these characters, and 
may be taken as the types of the genus as now restricted. 
Mr. Worthen, whilst describing a number of fossil fish remains found in Illinois, 
has adopted the same arrangement. The genus Chomatodus is retained by this 
accomplished ichthyologist, and the C. linearis, Agass., is taken as the type of the 
genus ; ten new species are then added from the sub-carboniferous limestone. The 
genus, as defined by Mr. Worthen, comprehends “teeth transversely much elon- 
gated, compressed and depressed, crown having the homologous parts of Petalodus. 
and the form and structure of Polyrhizodus—root short, sometimes obsolete, 
undivided.” 
Chomatodus linearis, Agass. 
(IAL IDX, mies, il, ‘iLe,)) 
Psammodus linearis—L. Agassiz, 1833. ‘‘Rech.surles Poiss. Foss.,” Vol. III., pl. xii., figs. 5-13. 
i. 5 P. de G. Egerton, 1837. “Catalogue of Foss. Fishes.” 
Chomatodus __,, L. Agassiz, 1840. “Rech. s. 1. Poiss. Foss.,” Vol. III., p. 108, pl. xii. 
figs. 5-13. 
D ¥ J. E. Portlock, 1843. ‘Geol. of Londonderry, &c.,” p. 446, pl. xiv., fig. 8. 
79 Ss C. G. Giebel, 1843. ‘Fauna der Vorwelt,” Vol. J., pt. 3, p. 341. 
5) » H. G. Bronn, 1848. ‘ Nomencl. Paleont.,” p. 293. 
% $6 A 1849. ‘ Enumerator Paleont.,” p. 647, 
% % J. Morris, 1854. “Cat. Brit. Foss.,” p. 321. 
es x F. J. Pictet, 1854. ‘ Traité de Paléont.,” Vol. IL., p. 266. 
,, (Helodus) ,, F. M‘Coy, 1855. © “ Brit. Paleeoz. Foss.,” p. 618. 
39 y Morrisand Roberts, 1862. “Quar. Jour. Geol. Soc.,” Vol. X VIII., p. 100. 
55 re Young & Armstrong, 1871. “Trans. Geol. Soc., Glasgow,” Vol. III., Supt., p. 69. 
R 32 eR es \ 1876. ‘Catalogue West. Scot. Foss.,” p. 60. 
> J. J. Bigsby, 1878. ‘Thesaurus Devon.-Carb.,” p. 349. 
»> ” L. G. de Koninck, 1878. “Fauna du Calc. Carb. de la Belgique,” p. 47, pl. vi., 
fig. 5. 
Teeth, medium size, average about three times as long as broad, median ridge 
depressed, straight or slightly curved; length 1:0 to 1:25 inch, breadth °3 of an 
