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



tcrior — being separated by a vertical line, and each bearing a thorn, that of the front 

 half being directed forwards, that of the hinder part backwards. The succeeding four 

 scutes which lie between this double one and the tail pedicle gradually diminish in 

 size, but each of them rises into a prominent backwardly curved and pointed thorn, of 

 a rather formidable appearance it must be owned. 



The dorsal Jin forms a small rounded projection from the outline of the back, and 

 is situated far behind, so as to be just in front of the tail pedicle. Its " rays " are simply 

 continuous with the scutes of the body, in fact they belong to the second lateral row, 

 but tend to become broken up distally. 



The caudal Jin is palseoniscoid in shape, being deeply cleft into two unequal lobes, 

 of which the upper is the longer and contains the prolongation of the body axis, from 

 the under aspect of which the fin-membrane exclusively arises. The body-prolongation 

 is covered by innumerable minute rhombic or spindle-shaped scales, which result from the 

 breaking up of the third, fourth and fifth series of lateral body-scutes. Along the dorsal 

 margin we have a special band of tiny narrow oblique scales, which would remind us 

 of the ridge-scales or " fulcra " of the upper lobe of a palseoniscoid tail, were it not that 

 the band here apparently consists of two rows of scales one above the other. The fin- 

 membrane is also covered with narrow scales which tend to be arranged linearly so as 

 to give the fin a very decidedly rayed appearance. All the scales of the tail and of the 

 caudal fin show the same minutely tuberculate ornamentation which occurs on the scutes 

 of the body. 



Position and Localities. — Extremely rare in the Ludlow horizon, one specimen only 

 having been found by Mr Tait in the " Ceratiocaris Band" at Shanks Castle, Logan 

 Water. It is, however, by far the most common of the fishes which occur in the over- 

 lying Downtonian rocks, and has been obtained in that horizon in the following localities 

 in Lanarkshire — Slot Burn, Seggholm ; Birkenhead Burn ;' Dippal Burn ; Monk's Burn. 

 Detached scales have also occurred in the Downtonian of the Pentland Hills, at Lynesiic 

 Burn, near its junction with the Lyne Water. 



Genus LASANIUS, Traquair. 



Generic Characters. — Elongated-fusiform in shape, with a deeply cleft heterocercal 

 caudal fin. A median row of ventral scutes, each bearing a recurved thorn, runs along 

 the ventral margin from behind the head to the origin of the caudal fin. Immediately 

 behind the head is a series of eight slender parallel bony rods on each side, and din 

 downwards and forwards, each of which at its dorsal extremity sends a process inwards 

 to the middle line of the back, there meeting its fellow of the opposite side. In front 

 of the anterior one of these rods, and parallel with it, is a chain of short slender ossicles. 

 No other hard parts are visible, but the form of the body is often more or less indicated 

 by a delicate carbonaceous film. 



[At first, judging from the position of the median aculeated scutes in Birkema, 



