130 



PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



[May 18, 



" There occurs in Orkney, in the neighbourhood of Kirkwall, and in 

 Caithness, in the neighbourhood of Thurso, a small Coccosteus which, 

 if not the young of Coccosteus oblongus, must be an undescribed 

 species." 



Letter dated April 3, 1848. 



" Your gutta-percha impression has sent me to my specimens ; 

 and I have at length succeeded in determining the true place of the 

 angular plate. In Agassiz's restoration of Coccosteus, tab. 6. fig. 4*, 

 there are five ventral plates, indicated by dotted lines, — four of them 

 lateral ventral, marked mm,nn, and a central lozenge-shaped plate 

 marked o. The anterior lateral ventral plates, mm, are, however, 

 nearly four times as large in both Coccosteus oblongus and Coccosteus 

 cu&pidatus as in the restoration (those of Coccosteus decipiens I 

 have not seen) ; and, instead of terminating at their upper extre- 

 mity at the top of the lozenze-shaped plate o, they run on to the 

 top of the omitted angular plate, the point of which rests in a 

 hollow scooped out of the top of the lozenge -shaped one. The 

 measurements of the plates in the following rude sketch (fig. 2), are 



Fig. 2. — Outline of the Plates of Coccosteus. 



taken from those of an actual specimen. Your specimen exhibits 

 the plates x and o, and one of the plates m; and the species 

 to which it belonged is, so far as I can determine the point, Coc- 

 costeus oblongus. The individual was small, smaller even than the 

 one whose ventral plates I have indicated in my draught, though 

 considerably larger than the Orkney and Thurso species to which 

 I referred in my communication of the 25th ult. The letter z 

 marks a pseudo -joint, which, judging from your gutta-percha cast, 

 is well marked in your specimen. Between the lateral ventral 



* Poissons Fossiles du Vieux Gres Rouge. 



