92 DR TRAILL ON FOSSIL FISHES FOUND IN ORKNEY. 



island of South Ronaldshey, which is twenty miles south-east from Skaill in a 

 direct line ; and I found a few scales like those of Kirkwall in the little island of 

 Papey-Westrey, which lies twenty-four miles north of the original quarry. From 

 these facts I have no doubt that attentive examination would detect fossil fishes 

 in many other parts of that group of islands. 



The generic character of Diplopterus is, 



Two equal dorsal fins opposite to two similar anal fins ; vertebral column 

 continued into the upper lobe of an even tail ; mouth wide, armed with strong 

 conical teeth. 



This fish belongs to the order Ganoidei, and to the second family of that 

 order, the Sauroidei. 



It is distinguished from Dipterus by the largeness of its mouth, and the form 

 of its tail ; from Palceoniscus by the double dorsal and anal fins, and the nearly 

 even extremity of its tail. I shall not attempt to anticipate M. AGASSIZ in a full 

 account of the Orkney Diplopterus, which I know he is fully prepared to describe ; 

 but content myself with stating, that this species may be known by its wide 

 mouth, rounded snout, and large head, which forms nearly one-fourth of its 

 whole length, and is covered with large scales. A single row of moderately large 

 trigonal scales, with posterior convex edges (giving them a somewhat hatchet 

 shape), passes along the ridge of the back ; and from their sides proceed rows of 

 lengthened rhomboidal scales obliquely downwards, diminishing in size from the 

 back toward the abdomen. The scales are neither groved nor granulated, but 

 covered with a smooth shining enamel. 



The dorsal and anal fins are large, rounded at their tips, and, like the lower 

 lobe of the tail, supported by numerous slender rays. 



