from the Neighhourhond nf Edinhnrgh. 205 



a sliglit notch on the posterior margin, and are evidently 

 obliqnely perforated by the Lateral slime-canal. 



Towards the dorsal and ventral margins the scales get 

 considerably lower ihan on the flanks. Those represented in 

 fig. 5 (also magnified two diameters) are from a situation 

 further to the front of the fish than those from which fig. .^ 

 was taken — namely, from the belly, a little distance behind and 

 })elow the suboperculum. In them the articular spine is very 

 broad and triangular, arising from the entire upper margin of 

 the scale, and showing besides a few peculiar grooves on the 

 .^surface, radiating from the middle of the base. 



The foregoing description of the configuration of the scales 

 has, together with the illustrative drawings, been principally 

 taken from impressions left on the hard ironstone after very 

 careful removal of the friable osseous matter, and from accurate 

 '' squeezes" in modelling-wax taken from the same. 



Conclusion. — From the foregoing description it is at once evi- 

 dent that the little fish just described belongs to the Palaeozoic 

 section of Dr. Young's suborder of Lepidopleuridaj ; but it can 

 hardly be included in any previously described genus. Neces- 

 sarily leaving dentition out of consideration, the shape of the 

 body and the relations of the dorsal fin alone widely distinguish 

 it from Mesolepis and Amphicentrum. From Platysomus it is 

 also separated by the form of the head, Avith its short blunt 

 snout and relatively more anteriorly placed orbit, as well as 

 by the nature of the scale-ornament, which in all the described 

 species of Platysomus consists of fine vertical or slightly 

 diagonal ridges or strife. In the typical Platysomi too (e. g. 

 PI. gihhosus, striatus) " the dorsal fin commences at the cul- 

 minating point of the dorsal ridge, and extends thence to the 

 upper lobe of the caudal fin, the component rays diminishing 

 very gradually in length from first to last ;" moreover it con- 

 tains "from 80 to 100 fin-rays"*; here, on the other hand, 

 the dorsal fin commences very much behind the highest point 

 of the back and contains considerably fewer rays, though their 

 exact number is not ascertainable. There only remains the 

 very imperfectly known genus Cleifhrolejjis, Egertonf, from 

 beds of doubtful Carboniferous age in. New South Wales, and 

 which, to certain points of resemblance to Platysomus, adds 

 the peculiarity of having a homocercal tail ; this organ, being 

 absent in our specimen, is not available as a means of compa- 

 rison. Although the rounded figure and posteriorly arisnig 

 dorsal fin of Cleithrolepis, added to Sir Philip Egerton's state- 



* Sir Philip Egerton, in * Quart. Journ. Geol. Soc. London,' 18C4, xx. 

 p. 3. 



t Lor. cit. p. 3, and pi. i. figs. 2 .t 3. 



