100 



NOTES AND ADDENDA. 



of the sides rhombic, coai'sely toothed on the posterior edges, and elabor- 

 ately sculptured with flat, scaly ridges, corresponding to the teeth of the 

 edge. The ridges are arranged in an upper and lower series, the latter 

 oblique to the former, so that each scale has the appearance of being com- 

 posed of two distinct portions. Lower surface of scales smooth, with a 

 few furrows corresponding to the ridges above, and the posterior edges 

 apparently serrate. Caudal scales narrowly rhombic, pointed, and with a 

 few central lines. The back is protected with about ten large oval scales 

 between the head and the dorsal. They are sculptured with waving lines, 

 curving with the edges, and are apparently truncate and serrate behind. 

 Tlie fish figured by Jackson, PI. II., Fig. 5, but not named, probably belongs 

 to the above species. 



Fig. 18. — Palceordscus modvhis, s.x. 



(a) Outline, natural size. 



(6) Series of Scales enlarged, seen from inside. The lower row are those on 

 mesial line. 



(c) Surface of exposed part of scale from side and from upper lube of tail, 



showing sculpture, enlarged. 



(d) One of the dorsal scales, enlarged. 



This beautiful and elaborately ornamented little fish is a perfect model 

 in miniature of that type of lower Carboniferous Pala'onii-cids to which it 

 belongs, and which has recently been separated by Dr Traquair in the 

 genus^ or subgenus Rliadiniddhys. For this reason I have given it the 

 specific name modulus. To the same genus belong the two next species, 

 described by Jackson, of which I shall give merely distinctive marks. 



P. Alberti Jackson, is larger than the preceding. The scales have more 

 numerous striaj. The dorsal scales are rounded posteriorly. The posterior 

 edge of the anal fin approaches nearly to the caudal, and extends consider- 

 ably behind the posterior edge of the dorsal. 



A specimen collected by Mr Ells, of the Geological Survey, indicates a 

 fish of the same general form with P. Alberti, but about 6 inches long. 

 The details are not sufticiently preserved to show if it diflers in these from 

 the above-named species. 



P. Cairnsii, Jackson.— About the same size with the last, but more 

 slender, and the head less obtuse in front. Scales thick and with few 



