222 Proceedings of the Boyal Physical Society. 



Pander refers to the body in question: — "Fig. 22. Ein 

 Ichthyoclornlithe, mit ausgezeiclmet schonen Sternen anf 

 beiden Flachen mid Kanten. Die Sternchen sind ausserlicli 

 von denen von Asterolepis, Coccosteus und Homosteus unmoglich 

 zu unterscheiden, aber die microscopische Structur ist ganz 

 verschieden. Knochenholilen fehlen ganzlich. Die Tuberkel 

 bestehen aus wahrer Dentine und die ganz innere Masse aus 

 einem Gewebe von Markcanalen, umgeben von concentrischen 

 Kreisen, in der Grundsubstanz, welche von den nach alien 

 Seiten ausstrahlenden feinen Zahnrohrchen unter rechten 

 Winkeln durchschnitten werden" (6, pp. 102, 103). From 

 this description, along with Pander's figure of the microscopic 

 structure (^&., fig. 34), the true nature of these bodies is, I 

 think, pretty evident. 



I am therefore quite unable to accept Prof. Trautschold's 

 views as to the " fins " of Coccosteus. 



But, as already mentioned, Prof, von Koenen has affirmed 

 the presence in Coccosteus of a " Euderorgan," and in his 

 restored 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 specimens of the genus. I have already stated 

 that the appearance here is strongly suggestive to my mind 

 that this " Euderorgan " or pectoral spine is nothing but the 

 outer Kante, 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. iii., 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 



