842 DR RAMSAY H. TRAQUAIR ON FOSSIL FISHES COLLECTED BY THE 



The median scutes are eighteen in number ; they are oblong in form when seen from 

 above or below, and the anterior extremity of each overlaps the posterior margin of the 

 one in front, a mode of imbrication with which we are unacquainted as regards the scales 

 of other fishes. Each of these plates is hollowed on its attached surface, elevated on its 

 free aspect, and there it is provided (figs. 10 and 11) with a sharp backwardly directed 

 thorn or aculeus. I have not observed any evidence of external sculpture in those 

 scutes. 



In a considerable number of specimens a delicate carbonaceous film indicates in parts 

 the remains of the soft tissues and gives a clue as to the external form of the fish. It is 

 thus clear that the head extended a little way beyond the oblique rods, and that it was, 

 as in Birkenia, bluntly rounded in front. In the same way the caudal fin is seen to 

 commence just at the posterior termination of the ventral row of scutes, and to be 

 heterocercal, deeply divided into two slender lobes, of which the upper one is consider- 

 ably the longer. This is well shown in fig. 8, but it is in the species next to be described 

 that the actual fin rays have been observed. 



As regards size, specimens have occurred so small as to have the row of ventral 

 scutes only three-quarters of an inch in length, whereas in large examples this may 

 extend over a length of two inches and a quarter. 



Position and Localities. — Only in the Downtonian horizon, in which it occurs in the 

 same localities with Birkenia, Lanarkia, etc. ; Birkenhead Burn ; Slot Burn, Seggholm ; 

 Dippal Bum ; Monk's Burn ; Smithy Burn, Hagshaw Hill. In the Pentland Hills 

 detached scutes have been found by Mr Tait at Lyneslie Burn, along with similar 

 scattered remains of Birkenia and Ateleaspis. 



Lasanius armatus, sp. nov., Traquair. 

 Plate V. figs. 12, 13. 



Specific Character. — Aculei of ventral scutes, thick and stout. 



Description. — Two specimens only have occurred, both of which are very small, the 

 more perfect one being only 1-| inch in length, including head and caudal fin, while the 

 other would probably have given the same measurement had it not been cut off by the 

 edge of the stone before the termination of the ventral scutes. 



The first mentioned specimen is represented in PL V. fig. 12, magnified three 

 diameters. It will be seen that the shape of the body is pretty well shadowed out by a 

 dark film, the form of the head being slightly distorted. I attach no significance to the 

 two round spots without film seen near the front of the head. The oblique rods are 

 seen in their proper position ; below them commences the ventral row of scutes, and 

 these are seen to have their thorns disproportionally large when compared with those of 

 L. problematicus. The shape of the individual thorns is better shown in the second 

 specimen, from which fig. 13 is taken, and which represents one of these plates with its 

 thorn seen from the side, and magnified four diameters. This difference in the ventral 



