﻿L28 ICHTHYODORTJLITES. 



Psammosteus paradoxus, Agassiz. 



L844. Psammolepis paradoxus, L. Agassiz, Poiss. Foss. vol. i. p. xxxiv. 



(name only). 

 1845. Psammosteus paradoxus, L. Agassiz, Poiss. Foss. V. G. P. 



p. 104, pi. B. figs. 5, 6, pi. xxvii. figs. 2-4. 



Type, Unknown. 



Form. Sc Loc. Devonian : N.W. Pnssia. 



P. 4491. Much abraded plate, with surface ornament partly re- 

 moved ; Eiver Ssjass. Purchased, 1884. 



P. 5959. Well-preserved portion of plate, 0*005 in thickness; 

 Juchora, Eiver Ssjass. In addition to a general fine 

 rugosity, the inner aspect exhibits a few short, small, 

 irregularly disposed grooves, with raised lateral borders 

 (cf. fig. of " AsteroJepis asmussi " in Pander's Placoderm. 

 devon. Syst. pi. vii, fig. 32). Purchased, 1889. 



Other plates have also been assigned to Psammosteus under the 

 folio whig names : — 



Psammosteus granulatus, F. M'Coy, Ann. Mag. Nat. Hist. [2] 

 vol. ii. (1848), p. 7. — Lower Carboniferous ; Kesh, Co. Fer- 

 managh. [Dublin Museum.] 



Psammosteus undulatus, L. Agassiz, Poiss. Foss. Y. Gr. P. (1845), 

 p. 106, pi. xxxi. figs. 11, 12 : Placosteus undulatus, 

 L. Agassiz, Poiss. Foss. vol. i. (1844), p. xxxiii (name 

 only). — Devonian ; N.W. Russia. 



Psammosteus vermicularis, F. M'Coy, torn. cit. p. 7. — Lower Car- 

 boniferous ; Fallaghloon, Maghera. [Dublin Museum.] 



The plate described as follows also exhibits some external 

 resemblance to Psammosteus, but its histological structure is un- 

 known : — 



Lophosteus superbus, C. H. Pander, Foss. Fische Silur. Syst. 

 (1856), p. 62, pi. vi. fig. 23. — Upper Silurian ; Ohhesaar, 

 Island of Oesel. 



In general external aspect the spines from the American Corni- 

 ferous Limestone named Acanthaspis (J. S. Newberry, Pep. Geol. 

 Surv. Ohio, vol. ii. pt. ii. 1875, p. 36) and Acantholepis (J. S. New- 

 berry, ibid. p. 38) are very suggestive of the triangular ichthyodo- 

 rulites assigned above to Psammosteus : their histological structure, 



