FISHES OF THE OLD RED SANDSTONE. 



599 



Dipterus macrolepidotus, Sedgwick and Murchison. (Geol. Trans, vol. iii. p. 143. PI. 15, 



16 and 17; Agass. vol. ii. p. 117.) 



The genus Dipterus was established by Cuvier from specimens which I sent to him from Caith- 

 ness in the year 1827- In the following year, Professor Sedgwick and myself having visited the 

 North of Scotland, we described the general structure of that country, including the black schists 

 and flagstones of Caithness, in which the Dipteri are contained, and we then expressed our belief, 

 that these strata were, in part, the equivalents of the Old Red Sandstone of England. That opinion 

 is now confirmed by independent zoological evidence, for I have since detected the above-named 

 species (which is very prevalent in the North of Scotland) in the lower beds of the Old Red Sand- 

 stone, at the Tin Mill near Downton Castle, Herefordshire. 



This genus was at first separated by Valenciennes and Pentland into 4 species (see Geol. Trans, 

 vol. iii. p. 143.), but after an attentive examination of a great variety of specimens, M. Agassiz, who 

 attempted to class these fishes in the genus Catopterus, has definitively concluded, that although 

 the genus Dipterus ought to be retained, the supposed four species are only differently modified 

 forms of the same animal. 



The generic character of the Dipterus, as now confirmed by M. Agassiz, consists in " Tivo 

 dorsal fins opposite to two similar anal fins, ivith a caudal fin conforming to that of the genus 

 Palceoniscus, in having the vertebral column prolonged into the extremity of the tail." 



Having as yet discovered small fragments only of the Dipterus in the Old Red Sandstone of the 

 Silurian region, I refer above to the figures of this genus in the Transactions of the Geological 

 Society, and to M. Agassiz's work, vol. ii. tab. 2a. p. 115. 



Holoptychus Nobilissimus, Agass. (PI. 2 bis. f. I, 2, 3, 4, 8 and 9 ?) 



• This splendid specimen, of which f. 1. is a reduced sketch and which measures 2 feet 4 inches by 

 12 inches, was discovered in the Old Red Sandstone at Clashbinnie, near Perth, North Britain, by 

 the Rev. James Noble, and was sent to me by him for the illustration of this work 1 . A drawing of 

 it having been forwarded to M. Agassiz, he has favoured me with the following description : 



" I am delighted with the fish represented in your drawing. It is a magnificent specimen, the 

 discovery of which is of great value in advancing my researches. I was previously acquainted with 

 fragments of several different species of the same genus, found at Gamrie and Burdie House in Scot- 

 land, and also in the coal-field of Staffordshire from which you sent me specimens. This individual, 

 however, will at length enable me to define precisely the characters of the genus which I named 

 Holoptychus from the folds of the scales. I had, it is true, seen detached scales of this species in 



i It is to my friend Sir John Robison, Sec. Roy. Soc, Edinb., that I owe the appearance of Holoptychus 

 Nobilissimus in this work. He presented a rough drawing of this ichthyolite to the British Association for the 

 Advancement of Science at the meeting at Bristol, on which occasion I was much struck by its form, and was 

 persuaded, that if properly described and examined by M. Agassiz, this splendid specimen would throw a new 

 light on the fossil fishes of the Old Red Sandstone. Sir J. Robison having explained these circumstances to 

 the Rev. J. Noble, that gentleman sent the original to my care, and thus M. Agassiz has been enabled to make 

 an important improvement in his description of certain forms belonging to this fine type, which previously 

 remained in obscurity or were assigned to other genera. 



4 g 2 



