OLD RED SANDSTONE FISHES. 



THE GEPHALASPID^. 



We commence this work with the consideration of the Eishes belonging to the 

 Eamily Cephalaspid^e of Professor Huxley/ because they are the oldest Eishes the 

 remains of which are known, — because these remains are of a special and peculiar nature, 

 having very little in common with the remains of the other Eishes of the Old Red 

 Sandstone, — and because a great deal of knowledge with regard to them has accumulated 

 since the last work, treating of them as a group, was published, viz., Agassiz's 

 'Recherches,' dating from the year 1834. 



§ I. History of the Cephalaspidee . — In his great work, ' Recherches sur les Poissons 

 Eossiles' (1835), Professor Agassiz established the genus Cephalaspis, to include four 

 species of Devonian Eishes obtained in Britain. These species were respectively named 

 C. Lyellii, C. rostratus, C. Lloydii, and C. Lewisii. The first was known to Prof. 

 Agassiz by specimens both from the West of England and from Scotland; and two of 

 these specimens showed, in addition to a large semicircular head-shield, the body covered 

 with scales and provided with a well-marked caudal fin. The other species were known 

 to him only by oval discoid bodies corresponding to the large semicircular head-plate 

 of the first; but he was led to conclude that they were allied forms partly by real, 

 partly by fancied resemblances in construction, and by their occurring under the same 

 conditions. He remarked, however, very strongly on the differences between the first 

 and the last of his species of Cephalaspis, and pointed out that, in addition to the differ- 

 ences in contour and shape, there were differences in minute structure and ornamen- 

 tation, which would probably lead at some future time to a separation of the species 

 into other genera. 



In 1847 Dr. Rudolph Kner published a memoir in Haidinger's ' Naturwissenschaft- 

 liche Abhandlungen,' for the purpose of proving that Cephalaspis Lewisii and C. Lloydii 

 were not the remains of Eisli at all, but that they were the internal shells of a Cephalopod 

 allied to Sepia, for which he proposed the generic title Pteraspis. 



Dr. Kner's conclusions were based upon the examination of a fossiP (evidently 

 closely allied to C. Lloydii) from the Upper Silurian (perhaps corresponding to our lowest 

 Devonian) strata of Gallicia. The structure of the test in this fossil was observed by 

 Dr. Kner to differ from that of any known osseous remains of Eishes ; and he considered, 

 from a somewhat superficial examination of both structures, that it agreed closely with 

 the cuttle-bone of Sepia. (See also p. 12.) 



In 1856 Dr. Eerdinand Roemer, in Dunker and Von Meyer's ' Palseontographica,' 



^ The Family Cepiialaspides of Agassiz included the Genera Pterichtliys, Coceosteus, &c. 

 2 Dr. Kner does not appear to have named this species, and I shall therefore hereafter speak of it a 

 Scaphaspis Knerii. (See pages 19 and 20.) 



