REPORT ON FOSSIL FISHES. 2 
“ey 
= 
Rhadinichthys delicatulus, sp. nov. 
Pl. II. figs. 6-9. 
Description.—Length from 14 to 3% inches ; shape and general proportions 
as in the last described species. 
The bones of the head and shoulder girdle are externally sculptured with 
delicate ridges, which, although they follow the same general pattern as in 
Rhadinichthys Geikiei, show less tendency to contortion and interruption, and, 
except along the dentary margin of the maxilla, are nowhere seen to break up 
into tubercles. The scales (figs 8, 9) are proportionately thinner, and those of 
the front part of the body have their upper and lower margins rather straighter 
and more parallel with the long axis of the body, but the same arrangement 
of low narrow scales is seen along the belly. The vertical grooves along the 
anterior margin of the sculptured area of the scales are almost lost, nearly the 
whole surface being covered with minute sharp ridges and furrows, which, with 
the exception of one or two which run parallel with, and close to, the 
inferior margin, are directed rather diagonally across the scale from before 
backwards, ending on fine denticulations of the hinder border; sometimes two 
of these ridges ending on one denticulation. Finally, this delicate ornament 
is in most cases continued back to the scales of the tail pedicle itself. The 
fins are similar in position, shape, and structure to those of Rhadinichthys 
Geikiei, but, comparing specimens of the same size, their rays seem to be 
rather more delicate, and more distantly articulated. One specimen (fig 6), the 
largest of the series, shows the strange phenomenon of the upper lobe of 
the caudal fin being neatly cut off and laid across the lower one. 
Remarks.—Rhadinichthys delicatulus so closely resembles the preceding 
species in structure and proportions, that I was for long in great doubt as to 
whether it were not better to treat it as a mere variety, or perhaps, seeing that 
the specimens are mostly of small size, as a young form, But so far as the 
collection goes, the differences between the scale-markings of the two forms 
are so constant that it is always easy to point out the specimens referable to 
the one and to the other. Moreover, small specimens, both from Colinton and 
Eskdale, which I believe to be referable to the young of Rhadinichthys Geikiei, 
have the scales always comparatively smooth, whereas in Rhadinichthys deli- 
catulus, the smaller the specimen, the more decided appears the distinctive 
pattern of the scale-markings. On these grounds I have decided to consider 
Rhadinichthys delicatulus as a “good species,” in the sense in which that 
term is usually employed. 
Position and Locality.—Near Glencartholm, Eskdale, in the Cement- stone 
group of the Calciferous Sandstone series. 
