Structure of Coccosteus decipiens, Agassiz. 135 



stored figure of his "subgenus" Brachydeirus (10, pi. iv. fig. 1) 

 he has represented the same as a long, pointed spine diverging 

 backwards from the antero-inferior angle of the antero-lateral 

 plate of the cuirass. In tab. ii. fig. 2 of the same work he has 

 also represented the spine in situ in a specimen of Coccosteus 

 Bickensis, v. Koen. ; but the supposed spine is here much 

 shorter than in the restoration, and lies horizontally just 

 below the antero-lateral plate, in the very spot where the 

 outer margin of the interlateral plate occurs in Scotch speci- 

 mens of the genus. I have already stated that the appear- 

 ance here is strongly suggestive to my mind that this 

 " Ruderorgan " or pectoral spine is nothing but the outer 

 Ka?ite, as the Germans would call it, of the interlateral plate. 

 But though the corresponding .part in C. decipiens is very 

 much shorter than that here represented, it attains a very 

 considerable proportional length as well as a very spine-like 

 appearance in C. minor, H. Miller, as is shown in my outline 

 figure of that species (13, pi. i. fig. 3). That it should also 

 attain similar proportions in other species is highly probable. 

 Of course I have not seen Prof. v. Koenen's specimens, 

 and it is not always safe to judge from figures and descrip- 

 tions alone. This much I am, however, entitled to say — that 

 if such a pectoral swimming-organ really does occur in Prof. 

 v. Koenen's species Bickensis, that species cannot be referred 

 to Coccosteus, in which no such organ is present. And, again, 

 if it is present in Brachydeirus bidorsatus, v. Koen., then 

 Brachydeirus is not merely a " subgenus " of Coccosteus, but 

 a genus with a very great distinction indeed. 



List of Works referred to. 



(1) Agassiz, L. — ' Monographic des Poissons Fossiles du vieux gres 



rouge.' Neufchatel, 1844-45. 



(2) Miller, Hugh. — ' The Old Red Sandstone, or New Walks in an 

 Old Field.' Edinburgh, 1841, and subsequent editions. 



(3) Duff, P.—' Sketch of the Geology of Moray.' Elgin, 1842. 



(4) Miller, H. — ' Footprints of the Creator, or the Asterolepis of 



Stromness.' Edinburgh, 1849. 



(5) M'Coy, F. — ' Systematic Description of the British Palaeozoic 

 Fossils in the Geological Museum of the University of Cambridge.' 

 London, 1851-55. 



(6) Pander, C. H. — ' Ueber die Placodermen des devonischen Sys- 



tems.' St. Petersburg, 1857. 



(7) Grey-Egerton, Sir P. de M.— " Palseichthyological Notes. — 



No. 12. Remarks on the Nomenclature of the Devonian Fishes," 



