﻿TCHTHYODOKULITES. 97 



Onchus cwvatus, C. H. Pander, Foss. Fische Siiur. Syst. (1856), 

 p. 70, pi. vi. fig. 29. — Upper Silurian ; Baltic Provinces. 



Onchus dubius, C. H. Pander, ibid. p. 71, pi. vi. fig. 28. — Ibid. 



Onchus jpennsylvanicus, E. W. Claypole, torn. cit. (1885), p. 61, 

 woodc. fig. 5. — Bloomfield Sandstone ; Perry Co., Penn- 

 sylvania. 



Onchus sublcevis, L. Agassiz, Poiss. Foss. V. G. R. (1845), p. 118, 

 pi. xxxiii. figs. 19-21. [Doubtfully assigned to 0. mur- 

 chisoni by E. von Eichwald, Leth. Rossica, vol. i. (1860), 

 p. 1595.] — Devonian ; St. Petersburg. 



Two doubtful Onchus-shsupedi fossils from tbe Lower Old Red 

 Sandstone of Abergavenny, Monmouthshire, are named Ptychacanthus 

 dubius, L. Agassiz, Poiss. Foss. vol. iii. (1843), p. 176, and Poiss. 

 Foss. V. G. R. (1845), p. 118, pi. xxxiii. figs. 22, 23. 



Very doubtful are Onchus compressus, E. von Eichwald (Leth. 

 Rossica, vol. i. 1860, p. 1595), previously figured without specific 

 name in Keyserling, Reise 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 0. deiveyi, J. Hall (Paleeont. New York, vol. ii. 1852, 

 p. 320, pi. lxxi. fig. 1), is a fragment of the Crustacean Ceratiocaris ; 

 it was obtained from the Niagara Group of Lockport and Rochester, 

 New York State. 



Another Devonian Ichthyodorulite, apparently related to Onchus, 

 has also been named as follows : — 



Naidas, L. Agassiz (Poiss. Foss. V. G. R. 1845, p. 116), with one 

 species, N. sidcatus, Agassiz (ibid. p. 116, pi. xxxiii. fig. 10), from St. 

 Petersburg. 



A very doubtful Devonian Ichthyodorulite from Petchora-Land 

 is also named Dimeracanthus concentricus, A. von Keyserling, Reise 

 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. Nat. Moscou, vol. xxv. (1852), pt. i. p. 174, pi. ii. 

 fig. 10. 



Genus CTENACANTHUS, Agassiz. 



[Poiss. Foss. 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. H 



