600 



FISHES OF THE OLD RED SANDSTONE. 



the possession of Professor Jameson and Dr. Buckland, but so imperfect, that before I was ac- 

 quainted with those of Gamrie, which convinced me of my error, I intended to refer them to my 

 genus Gyrolepis. Compare my chapter on Gyrolepis, (p. 172. 5 liv.), and particularly the article 

 Gyrolepis gig aniens, which is the fish you have sent me, and the name of which must now be 

 changed." (The figures of it have, fortunately, not yet appeared.) M. Agassiz then proceeds to 

 show that the fish in question has no relation to the accipenser or sturgeon with which it had been 

 compared. "No sturgeon has similar scales. In the genus Accipenser there are only 5 rows of 

 c ecussons' scutcheons upon the back and sides, whilst this specimen proves that the whole surface 

 of the Holoptychus was covered by them, as, indeed, I had perceived in various specimens found at 

 Burdie House and Gamrie. Not one, however, of these species had conveyed to me so complete an 

 idea of the characters of the genus as your specimen; and since, for the reasons assigned, its generic 

 name must be changed, I see no inconvenience in also changing the name of the species, and in 

 adopting, instead of gig aniens, that which you suggest in honour of the discoverer, Mr. Noble, 

 {Holoptychus Nobilissimus) ; the more so, since the species found in the carboniferous deposits at 

 Burdie House is of as gigantic dimensions as that of the Old Red Sandstone." 



"The generic characters consist in the peculiar structure of the scales, the enamelled surface of 

 which is marked by large undulating furrows. Another characteristic feature is in the distant po- 

 sition of the ventral fins, far removed towards the tail, and much nearer the anus and anal fin than in 

 any other genus of the family of Ganoids. Lastly, the arrangement of the branchial ' branchiostegues' 

 rays is very remarkable, for they form two large plates between the branches of the inferior jaw, as 

 in the genus Megalichthys. They are perfectly well seen in this specimen, and are of a triangular 

 shape. What is perhaps most striking in this Old Red species, is the small size of the head in com- 

 parison with the body; for the outline of the two branches of the inferior jaw, which are narrow, 

 are so clearly seen as to enable us to judge of the size or rather length of the head, which was cer- 

 tainly short and obtuse. The structure of the f nageoirs,' the rounded form of the ventral fin, 

 and the manner in which the rays of its anterior edge are insensibly prolonged, coupled with their 

 relative thinness, are also very marked distinctions, and the same may be said of the anal fin 

 and the disposition of its anterior edge. It is to be hoped we shall at some future day discover 

 a specimen, placed in profile, which will enable us to decide the position of the dorsal fin and the 

 fin of the tail. (The tail is wanting in this specimen.) This individual is lying on its back, and the 

 attitude is very expressive; for it proves that the fish was naturally of a depressed form, ' plutot 

 deprime que comprime,' and not compressed by force. In fact, whenever flat fish are found placed 

 on their backs or bellies in the rock their scales are always deranged, and it is only when they are 

 naturally very round, or even depressed (deprime), that the ventral scales preserve their natural po- 

 sition as in this example." 



In Plate 2 Ms., a ventral scale of II. Nobilissimus, natural size, is given, f. 2. Fig. 3. is pro- 

 bably a scale or portion of the operculum, also of natural size; and being found in the same quar- 

 ries of Clashbinnie, is also supposed to belong to II. Nobilissimus ; as well as the very remarkable 

 form, f. 4, which exhibits the toothed processes beneath the scales. 



Does the tooth (PI. 2 bis. figs. 8 and 9.) belong to this genus or to Megalichthys ? It was found 

 with other remains of fishes (such as large scales of Holoptychus, figs. 2 and 3), four miles to the south 

 of Elgin, by Mr. Martin of that town, who, together with the Rev. G. Gordon, has made consider- 

 able collections of the ichthyolites of that neighbourhood. These remains occur in pretty highly in- 

 clined strata of coarse, slightly calcareous conglomerate, very low in the system of Old Red Sandstone, 

 for the beds dip under the cornstones of Murrayshire, described by Professor Sedgwick and myself. 



