TCHTHYODORTJLITES. 
97 
Onchus Gurvcitus , 0. H. Pander, Foss. Bische Silur. 8yst. (1856),^^ 
p. 70, pi. vi. fig. 29.—Upper Silurian; Baltic Provinces. 
Onchus clubius, C.. H. Pander, ibid. p. 71, pi. vi. fig. 28.—Ibid. 
Onchus pennsylvanicus , E. W. Claypole, tom. cit. (1885), p. 61, 
woodc. fig. 5.—Bloomfield Sandstone ; Perry Co., Penn¬ 
sylvania. 
Onchus sublcevis, L. Agassiz, Poiss. Boss. Y. G. E. (1845), p. 118, 
pi. xxxiii. figs. 19-21. [Doubtfully assigned to 0. mur- 
chisoni by E. von Eichwald, Leth. Eossica, vol. i. (1860), 
p. 1595.]—Devonian.; St. Petersburg. 
Two doubtful Ou<?7ms-shaped fossils from tbe Lower Old Eed 
Sandstone of Abergavenny, Ytonmouthshire, are named Ptychacanthus 
dubius , L. Agassiz, Poiss. Eoss. vol. iii. (1843), p. 176, and Poiss. 
Boss. Y. G. E. (1845), p. 118, pi. xxxiii. figs. 22, 23. 
Very doubtful are Onchus compressus, E. von Eichwald (Leth. 
Eossica, vol. i. 1860, p. 1595), previously figured without specific 
name in Keyserling, Eeise in das Petschoraland (1846), p. 291, 
pi. xxi. fig. a, from so-called Permian, Kischerma, Petchora-Land ; 
and 0. tricarinatus , C. H. Pander (op. cit. p. 71, pi. vi. fig. 30), 
from the Silurian of the Baltic Provinces. 
The so-called O. cleiueyi , J. Hall (Palseont. Hew York, vol. ii. 1852, 
p. 320, pi. lxxi. fig. 1), is a fragment of the Crustacean Oercitiocaris; 
it was obtained from the Hiagara Group of Lockport and Eochester, 
Hew York State. 
Another Devonian Ichthyodorulite, apparently related to Onchus , 
has also been named as follows :— 
Naulas , L. Agassiz (Poiss. Boss. Y. G. E. 1845, p. 116), with one 
species, N. sulcatus, Agassiz (ibid. p. 116, pi. xxxiii. fig. 10), from St. 
Petersburg. 
A very doubtful Devonian Ichthyodorulite from Petchora-Land 
is also named Dimeraccinthus concentricus, A, von Keyserling, Eeise 
in das Petschoraland (1846), p. 292 b ; and another from the Go¬ 
vernment of Orel is termed Pycnacanthus, G. Fischer de Waldheim, 
Bull. Soc. Imp. Hat. Moscou, vol. xxv. (1852), pt. i. p. 174, pi. ii. 
fig. 10. 
Genus CTENACAMTHUS, Agassiz. 
[Poiss. Boss. vol. iii. 1837, p. 10.] 
Dorsal fin-spines robust, often attaining to a'large size, laterally 
compressed; sides of exserted portion ornamented with longitudinal 
ridges, usually crenulated or denticulated, rarely smooth; posterior 
part ii. * n 
