THE DERBIO. 25 



for the development of these markings. Cuvier regards 

 the Lichia tetracantha discovered by Mr. Bowdich near 

 the Gambia as merely a variety of this species, but from 

 a drawing of tetracantha made at Sierra Leone by Dr. 

 Mitchill, Surgeon in the Royal Navy, it appears to be a 

 considerably more oblong species, and instead of about 

 four spots on the fore part of the sides, there is a series 

 of ten smaller ones, extending nearly to the base of the 

 caudal. Its colour is bright ultramarine blue, and silvery 

 white below, the lateral spots being darker blue, and the 

 tips of the fins blackish-blue, as in glaucus. The true 

 glaucus was also obtained by Dr. Mitchill, off the Niger 

 in the Bight of Benin, and his drawing represents it as 

 of a darker blue than tetracantha, and of a considerably 

 deeper oval form. The following description of the 

 Derbio is drawn up from the photographs, with additions 

 furnished by Mr. Couch. 



This gentleman states the length of the specimen to 

 have been thirteen inches and a half, and its height three 

 inches and seven-eighths. The comparative length, omit- 

 ting the acute caudal lobes, is thrice the height ; and the 

 head forms a sixth part of the total length, including the 

 whole caudal fin. The scales are small, and not strong. 

 The cheeks nacry and scaleless. The lateral line descends 

 obliquely without an abrupt curve from the suprascapular, 

 till it comes nearly over the first free anal spine, and a 

 little above mid-height, and from thence runs straight to 

 the central rays of the caudal fin without any keeling or 

 armature perceptible in the photograph. 



The fin formula is 



D. VI. 1 + 22: A. II. 1 + 23 or 24. 



The ventrals and pectorals are both small. There is a 

 couchant spine pointing forwards before the first dorsal, 

 which is composed of six detached spines, all nearly of 



