PERCARIXA DP^JIIDOFFIl. 



:3L 



Percarina demidof&i (Nordmann). 



1 D. 10, 2 D. 8/9—10, A. 2/9—10. 



This species (Fig-. 11) is the only example of the genus ; it is characterised 

 by a line of round black spots along the back, and a lunate brown spot on 

 the neck. All the fins are transparent, and without spots. It differs from 

 Acerina, and resembles Lucioperea in possessing two closely-connected dorsal 

 fins. The body is moi-e compressed from side to side than in Acerina 

 cenina. Its g-reatest height is at the first dorsal fin, and is twice the thick- 

 ness of the fish ; the height is also equal to the distance from the extremity 

 of the snout to the margin of the pre-operculum. The entire length of the 



Fig. 11. rEKfAllIXA DEMIDOFl'II (NOUDM ANX) . 



animal is three and three-quarter times the length of the head. The eye 

 is larg-e, separated from the snout by its own diameter^ and the inter-orbital 

 space , is two-thirds of the orbital diameter. The mouth is wide; it reaches 

 back to beneath the middle of the eye. The pre-maxillaries are prolonged 

 to form the extremity of the jaw, and carry fine densely-placed teeth through- 

 out their length. The lower jaw has not only a small band of villiform 

 teeth along its upper edges, but the teeth are produced on both sides, so that 

 the lower jaw is covered with villiform teeth, like a spinous cylinder — a form 

 of dentition which is not known in any other fish. The vomer is provided 

 with only a small group of teeth. The operculum is less developed than in 

 Acerina cernua, but posseses a similar spine. The pre-operculum along 

 its entire length has i\\Q aspect of being double, there being two parallel 

 spinous borders, between which the branch of the cephalic canal is con- 

 tained which is supplied to the lower jaw. Owing to the wide gape of the 



