On the Fossil Fishes of the Carboniferous Limestone Series of Great Britain. 458 
the arrangement of the teeth, or whether they formed only a part of a larger series. 
As almost always happens with the remains of the Klasmobranch fishes, the teeth 
become detached and separated during the period of their decomposition, and it is 
almost impossible to correctly infer any relation of one to another when found fossil, 
under such circumstances. 
Of the Helodi already described it is probable that several species, such as H. 
turgidus, were the median teeth of Cochliodus. This willalso apply to most of the 
America specimens. A second type, of which H. planus may be taken as an 
-example, has been proved to belong to a distinct genus of fish, and there is 
no doubt so far as H. planus is concerned that it is the inside tooth of Psephodus 
magnus. Capt. T. Jones, in a letter to Portlock, published in the Geological Report 
of Londonderry, &c., p. 462 (1848), was the first to point out the relationship of H, 
planus to Cochliodus (now Psephodus) magnus. He considered that the one passed 
into the other. Specimens in the Enniskillen collection show that the two teeth 
were attached to each other in the same jaw. 
It does not appear probable that any of the teeth of Helodus were associated 
with those of Psammodus, or that the former stands in the relation of a subgenus 
of the latter, as mdicated by M‘Coy. There is no evidence of such near relation- 
ship, and the general similarity of the porous surface of the teeth relied on by 
M‘Coy, would indicate a relationship with several other genera, quite as reasonably 
as with that of Psammodus. . 
Helodus crassus, Davis. 
@L IDIDS, mes, i, 2,) 
Psammodus cinctus (pars) —L. Agassiz, 1833. ae ne Foss.,” Vol. IIT., pl. xv., fig. 
” x Fy P. G. Egerton, 1837. ‘Cat: Hoss. Fishes.” 
Chomatodus __,, 5. L. Agassiz, 1838. ‘‘ Rech. Poiss. Foss.,” Vol. ILI., p. 107. 
» » ” J. E. Portlock, 1843. “Geol. Londonderry,” p. 467, pl. xiv.a, fig. 9. 
” 5) 55 C. G. Giebel, 1848, ‘“ Fauna der Vorwelt,” Vol. I., pt. 3, p. 341, 
» p rr H. G. Bronn, 1848. ‘Nomencl. Paleont.,” p. 292. 
” ” x ss 1849. “ Knumerator Paleont.,” p. 647. 
»” ” . J. Morris, 1854. “Cat. Brit. Foss.,” p. 321. 
” ry) »” F. J. Pictet, 1854. <“'Traité de Paléont.,” Vol. IT., p. 266. 
», (Helodus), ,, F. M‘Coy, 1855. “Brit. Palzoz. Foss.,” p. 617. 
” » 99 Morris and Roberts, IGOR, & pia Journ. Geol. Soc.,” Vol. XVIII, 
p- 
» » % Enniskillen, 1869. ‘Cat. Types Foss. Fish.,” p. 4. 
» ” ” Young and Armstrong, 1871. “Trans. Geol. Soc., Glasgow,” Vol. IIT., 
Supt., p. 69. 
‘s zs ‘ Berea \ 1876. “Cat. W. Scot. Foss.,” p. 60. 
» » » J.J. Bigsby, 1878, “Thesaurus Dev.-Carb.,” p. 349. 
» » » L. G, de Koninck, 1878, “Fauna du Cale. Carb. de la Belgique,” 
p. 46, pl. iv., fig. 3, pl. vi., figs. 1-5. 
