Devonian Fish-Fauna of 8j)itzl>ergen. 15 



Eifel. There is a large keeled ])late of a very similar eliarac- 

 ter from the neighbourhood of Gerolstein in the Museum of 

 Comparative Zoology, Cambridge (Mass.) ; and evidence is 

 gradually accumulating to prove that certain of the Ostraco- 

 dermi attained comparatively gigantic proportions. 



EXPLANATION OF THE TLATES. 

 Plate I. 



Fii). 1. Acanfhftspis dccipieiis, sp. n. ; associated dorsal (a) and ACiitriil 

 (b) shields. Lower Devonian, Dickson Bay. a.v.L, anterior 

 \entro-lateral ; 5, basal plate of pectoral appendag-e ; o, impres- 

 sion of ridge and constriction on the visceral aspect of the pos- 

 terior ventro-laterals; m, lonoitudinal lateral ridge (and supposed 

 suture) on the dorsal shield; ?«.«., median ventral ; ^).y./., pos- 

 terior ventro-lateral ; s, pectoral appendage ; x, pair of descend- 

 ing processes on visceral aspect of dorsal shield ; y z, line of 

 transverse section, fig. 2, 



Fiff. 2. Ditto ; transverse section of dorsal shield of the same specimen, 

 along ;/ z. 



Fi(/. 3. Ditto ; two transverse sections of the pectoral appendnge of the 

 same specimen, one («) nearer the base than the other (h). 



Plate II. 



Fi(j. 1. rteraspis Nathorsti, Lank. ; hinder portion of ventral sliield, 



visceral aspect. Lower Devonian, Dickson Bay. 

 Fig. 2. Acanthasjn's minor, sp. n. ; portion of occipital plate, visceral 



aspect, twice nat. size. Lower Devonian, Dickson Bay. p, 



median process of hinder border. 

 Fi(/. 3. Ditto ; portion of pectoral appendage, associated with above, 



twice nat. size. 

 Figs. 4, 5. Ditto ; two plates of the same, twice nat. size, outer and inner 



aspect respectively. 

 Figs. G-10. Porolepis posnaniensis (Kade) ; scales. Lower Devonian, 



Klaas Billen Bay. Fig. G is inner aspect, nat. size ; the others 



exhibit the outer aspect, twice or thrice nat. size. 

 Fig. 11. Fsdnunosteus arenatiis, Ag. ; portion of bent plate, front view 



and transverse section (a). Fig. Wb. Abraded tubercles of 



flat plate of ditto, enlarged. Upper Devonian, Mimers Valley. 

 Fig. 12. Onychodus arcticus, A. IS. Woodw. ; presymphysial bone, twice 



nat. size. Upper Devonian, Mimers Valley. 



Plate III. 



Fig. 1. Asterophx scabra, g. et sp. n. ; cranial shield. Upper Devonian, 

 Mimers Valley, o, Op median plates ; 1, 2, posterior and ante- 

 rior paired plates ; x, facial plate ; y, z, undetermined plates. 



Fig. 2. Ditto ; problematical bone exhibited on the inferior aspect of the 

 same specimen, two thirds nat. size. 



The specimens are all preserved in the Royal Swedish State Museum, 

 Stockholm, ajid unless otherwise stated the figures are of the natural size. 



