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TOHTHYOnOKFLITES. 



Genus PSAMMOSTEUS, Agassiz. 



[Poiss. Fobs. V. G. E. 1845, p. 103.] 



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

 only). 

 Psammolepis, L. Agassiz, ibid. p. xxxiv (name only). 



Spines and dermal plates of moderate size, the former much 

 laterally compressed, usually unsymmetrical, broad and triangular, 

 with a large internal cavity and short base of insertion. External 

 surface ornamented with numerous, closely arranged, rounded or 

 elongated tubercles of gano-dentine, usually stellate and rarely 

 arranged in regular series. 



As pointed out by Agassiz and Pander, the histological structure 

 of these ichthyodorulites is suggestive of that of Selachian dermal 

 armour ; and in external characters they are most nearly paralleled 

 by Oracanthus, as described below. 



Psammosteus mseandrinus, Agassiz. 



1844. Placosteus m<sandrinus, L. Agassiz, Poiss. Foss. vol. i. p. xxxiii 

 (name only). 



1845. Psammosteus mceandrinus, L. Agassiz, Poiss. Foss. V. G. R. 

 p. 104, pi. xxvii. figs. 5, 6. 



1845. Ctenacanthus serrulatus, L. Agassiz, ibid. p. 119, pi. xxxiii. fig. 24. 



1857. Aster olepis ?, C. H. Pander, Placoderm. devon. Syst. p. 20, pi. vii. 

 figs. 16-18. 



1858. Psammosteus m&andrinus, G. Kade, Programm k. Realschnle zu 

 Meseritz, p. 11, figs. 2-5. 



1860. Psammosteus mceandrinus, E. von Eichwald, Leth. Eossica, vol. i. 



p. 1516. 

 1880. Coccosteus megalopteryx, H. Trautschold (error e), Verhandl. russ. 



k. mineral. Gesell. St. Petersburg, p. 152, pi. vi. fig. 1, pi. vii. fig. 2. 



1889. Coccosteus megalopteryx, H. Trautschold (errore), Zeitschr. 

 deutsch. geol. Gesell. vol. xli. p. 36. 



1890. " Selachian appendages," E. H. Traquair, Ann. Mag. Nat. Hist. 

 [6] vol. v. p. 134. 



Type. Unknown. 

 The type species. 

 Form. &( Loc. Devonian : N.W. Eussia. 



P. 4493. Two spines, imperfect distally, of the form assigned to 

 this species by Eichwald, but described as Coccosteus 

 meg alopter yoc by Trautschold ; from banks of Eiver Ssjass. 

 In one specimen there are indications of a narrow inserted 

 portion at the base of one side and a much deeper insertion 



