1869.] EGERTON GYRODTJS. 383 



viz. the Oxford clay, Cornbrash, &c. This is just the period in which 

 the genus Gyrodus seems to have attained its maximum develop- 

 ment. jSTo species has yet been discovered in the Trias or Lias. 

 A few occur in the Lower Oolites, from which period the genus 

 expands enormously through the remainder of the Oolitic series, 

 decreasing again in the Wealden, and finally disappearing in the 

 Cretacean era. I have named this species Gyrodus Goweri in 

 recognition of the great interest the Duke of Sutherland takes in all 

 questions affecting the county of Sutherland, which has been re- 

 markably shown by his establishing a museum at Dunrobin Castle for 

 the reception of specimens of science and antiquity connected vd\h. 

 the county, for the amusement and instruction of those who visit the 

 charming scenery of the neighbourhood of Golspie. 



2. Gyrodus coccoderma, Egerton. 



The Museum of Practical Geology possesses a portion of a large 

 Pjcnodont fi^h referable to the genus Gyrodus, from the Kim- 

 meridge Clay of Kimmeridge. The specimen is a mere fragment, 

 containing only a group of scales from the nuchal and dorsal re- 

 gion, above the lateral line, and before the dorsal fin. It mea- 

 sures 1 foot in length by 7 inches in depth. Judging from 

 the proportions of other species of the genus Gyrodus, this fish, 

 when perfect, must have been at least 30 inches in length, from the 

 snout to the commencement of the tail, by 20 inches in depth, 

 rivalling in size the great Gyrodus rJiomhoidalis of the Munich 

 Museum. 



It contains twelve dorso -lateral series of scales, with eight scales 

 in each row, measuring each 1 inch in antero-posterior diameter. 

 They vary in depth and form according to the position they occupy 

 in the series. Those nearer the top of the back are the shortest, 

 and are lozenge-shaped ; the succeeding scales in each row become 

 more elongated in descending order, so far as they are preserved. 

 The scales of the flanks are unfortunately not present ; they would 

 probably have been from 2| to 3 inches in length. The surface- 

 ornament of the scales (fig. 3) is well seen, and is very peculiar. 

 It consists of a multitude of symmetrical granules of hard and 

 lustrous ganoine, like grains of millet-seed, irregularly scattered 

 over the surface. On the nape and back they are thickly grouped, 

 but more sparsely sprinkled over the other parts. Each granule 

 maintains its form, even where they are most crowded, and has no 

 tendency to coalesce with its neighbours to constitute the meandrine 

 pattern so frequently found on scales with raised patterns. It 

 differs in this respect from Gyrodus Goweri and Gyrodus rJiom^ 

 hoidalis, but somewhat resembles a little-known species from the 

 Oolite of Stonesfield, named by Agassiz Gyrodus perlatus — the arti- 

 culating processes of the scales forming the dermal ribs, and being 

 very strong, and coarsely striated longitudinally. They measure half 

 an inch in length. I have given the specific title coccoderma to this 

 fish, from the characteristic features of the scales. 



