710 DR RAMSAY H. TRAQTJAIR S DESCRIPTION OF 



In his " Poissons Fossiles," Agassiz has said very little about the bones of the 

 head of Eurynotus, merely noticing the narrow shape of the operculum and sub- 

 operculum, and the proportionally great height of the latter, also observing a 

 triangular plate which he considered as a suborbital bone ; lastly, that the teeth 

 were small and obtuse. I regret that my knowledge of the osteology of the head 

 of this fish is very imperfect ; what I do know of it is derived from specimens of 

 Eurynotus fimbriatus from Wardie, and in figs. 8 and 9 I have sketched the 

 forms of the various bones I have been able to make out. 



Regarding the cranium proper I can say nothing, the specimens being too 

 much crushed. 



The operculum is very small in proportion to the size of the fish, and is of a 

 short oblong form, with the posterior-superior and anterior-inferior angles some- 

 what rounded off. The suboperculum is larger, but also oblong in form ; its upper 

 margin is concave ; the posterior-inferior angle is very much rounded off ; a 

 diagonal line from the posterior-superior to the anterior-inferior angle divides the 

 external surface into two areas ; and of these the upper one is ornamented by 

 ridges radiating from the anterior-inferior angle of the bone, while the lower area 

 is marked by concentric ridges running parallel with the rounded posterior-inferior 

 margin. In front of the two plates just described is another elongated one which 

 certainly seems to represent a preoperculum. The superior maxillary bone (22, 

 figs. 8 and 12) is most decidedly different from that in Amblypterus and Pygop- 

 terus, consisting of an elongated triangular plate with the apex directed forwards. 

 The lower margin, which is the longest, is seen to be garnished along the whole of 

 its inner edge by small rounded polished teeth, which resemble nothing so much as 

 small and somewhat flattened grains of shot. They are placed irregularly together, 

 the largest ones being about the middle of the series ; about one-third from the 

 anterior extremity of the bone they suddenly become excessively minute, and at 

 the same time are not placed so close together. Some are observed to be rather 

 narrowed at the base, but this is not universal. The border next in length is the 

 upper, which slopes towards the apex in front. The short side is posterior, and 

 fits on in front of the plate which I have considered the preoperculum. The 

 external surface of the superior maxillary bone is sculptured by coarse ridges 

 which run parallel to the posterior and upper margins. 



Lying on the same piece of stone with the superior maxillary bone, from which 

 fig. 12 has been taken, is a flat irregularly shaped bone (fig. 13), which must 

 appertain to the palate. It is undefined at one extremity, and passes into two 

 irregular processes at the other. A large portion of its surface is completely 

 covered by the rounded teeth already described, and which are indeed so thickly 

 placed together, that in many instances their bases assume a polygonal form. 

 The part of the bone bearing the teeth is marked by three longitudinal ridges 

 bounding two shallow furrows. Two of those ridges form the margins of the 



