112 



ECHENEIS. 



TnT3 genus is recognised by having a flat oblong disk on the top of 

 the head, which is marked with a double row of transverse raised 

 lines or ridges, each of which is furnished with spinous teeth, the 

 whole enclosed within a raised border. There is in addition a single 

 dorsal and anal fin, and the ventral fins are thoracic. 



There are several species of this genus, but there is reason to suppose 

 they have been represented as more numerous than they are, for it 

 appears from the observations of Dr. Albert Giinther, in the "Annals 

 of Natural History," March 1860, that the number of plaits or larainso 

 in the disk or sucking apparatus on the head is subject to variation, 

 and in consequence that a separation of species built on such variation 

 will lead to error. It appears also that the exact form of the tail is 

 uncertain as a distinction; for it is found to vary from the forked 

 shape to the round in what may be termed the Common llemora, as 

 the lamina) vary also in the same fish from sixteen to twenty. 

 Eoughness of the tongue has also been thought a specific character; 

 but in the same undoubted species this has been seen to vary from 

 a state of smoothness to decidedly rough. 



All the fishes of this genus may be considered as being only furnished 

 with a single dorsal fin; but an attempt has been made to represent 

 the sucking apparatus as in its nature an anterior dorsal fin, although 

 for special purposes it is made to assume a different form from ordinary 

 fins. It is the opinion of Yoigt that this modification is accomplished 

 by the bending of the rays downwards on both sides, to constitute the 

 disk with its lamina3, and that the very small hooks which are on the 

 borders of the laminae have the same function as similar formations 

 have in the several species of the family of Belistes. It is beyond 

 doubt that there are examples in nature where an organ by even an 

 apparently small change of structure is rendered capable of performing 

 functions which appear very different from those for which it seemed 

 originally intended; but more extended examination must be instituted 

 before this can be considered certain in the present instance; and if 

 there be at all a resemblance to a fin in this organ, it would rather 

 appear to be in the raised border of the disk than in the laminae, the 

 structure of which appears to be of the nature of cartilage, and which 

 rest on a scries of bones that communicate with the spinous or upright 

 processes of the vertebrae, and ai*e themselves moved by iiidopeudent 

 muscular fibies'. Tliese laminae are in pairs, proceeding from a middle 

 longitudinal ridge, and in tliis respect diff'er greatly from the fins of 

 any known fishes. When about to bring this sucking organ into 

 action, the fish a]>pears to bring the hooks or rough edge of these 

 laminae into contact with the surface on which it is its purpose to fix 

 itself; and then, chielly by means of the raised border of the disk, 



