138 



THE GEOLOGIST. 



nally by small hexagonal ganoid scales. Near the centre of this shield 

 two rather closely placed holes formed the orbits for the eyes. In one 

 of the heads in my possession the eye-balls are finely preserved 

 completely petrified ; between the eyes were two ridges having an 

 intermediate hollow or sinns extending from the eyes backwards. 

 One of my specimens shows that these ridges united towards the 

 posterior edge of the shield, forming evidently a strong defence. 

 None of the many heads I have examined show the slightest evidence 

 that this creature was possessed of teeth, or a month of the ordinary 

 form ; this organ, I believe, being similar to the sturgeon, which, royal 

 fish, I have little doubt, had this comparatively small creature as its 

 representative in these old world waters. Some of the cusps or 

 sharpened points of the shield are very much elongated and toothed 

 on the interior of the margin. The body as compared with the head 

 was but small, very slender, and protected by bony rings, extending 

 in a slanting direction from the back downwards, these again being 

 covered by exceedingly minute rhomboidal scales ; in this respect 

 resembling the larger number of the fishes found in the lower beds of 

 the Forfarshire Old Red, as Glimcdius, Acanthodes, DvplaGamthus, &c. 

 In only one specimen have I ever observed these on all scales ; but a 

 portion of one in my possession shows a very perfectly preserved 

 cast of them : its heterocercal tail was much produced and furnished 

 with a very large and powerful fin. None of the specimens I have 

 as yet examined show the slightest vestige of either anal or ventral 

 fins. The existence of a dorsal is by no means established ; had it 

 existed it must have occupied a position very far back. This creature 

 was, however, further remarkable for having two very large membra- 

 nous pectorals, attached immediately under the cephalic buckler, 

 seemingly of a leathery consistence, and covered by small sub-circular 

 or hexagonal scales. The pectorals were first discovered by me, in 

 the specimen from which the figure is copied. 



The remains of Cephalaspis, generally associated with, plates or 

 other portions of the Pterygotus Anglicus, have been found in alnost 

 nil the places where the grey flagstones, generally known in commerce 

 :» s 1,1,1 Arbroath pavement, and which crop out" in so many localities 

 in Forfarshire, have been wrought. It has also been found in a bright 

 red micaceous sandstone, overlying and considerably above these 

 flagstones, while in no case has the Pterygotus Anglicus been, up to 

 this bime, found in the sandstones overlying the shales and flagstones 

 ofthe Arbroath pavement. Although the above-mentioned flagstones 

 are (married in so very many places in Forfarshire, anything ap- 

 proaching to a complete specimen of this fish very rarely turns up 

 indeed, I only know of some eight or ten specimens showing the 

 body, having been as yet disinterred from the rocks in which they 

 have so long been intombed. Perhaps the finest of these was several 

 years ago got by the late Mr. Lindsay Carnegie from his quarries at 

 Leysmill, and by him presented to the Arbroath Museum. The well- 

 known specimen presented by Sir Charles Lyell to the British 

 Museum was found in a quarry near the village of Glanmis. There 



