

GREAT BRITAIN. 321 



icncc the name of the sub-class), destitute of true jaws, 

 id capable of being employed as a sucker. The body is 

 nig, cylindrical, and somewhat compressed posteriorly. 

 \eth. The mouth, which is sub-inferior and surrounded 

 y - a circular lip, has maxillary, mandibular, suctorial and 

 ngual teeth, all of which are of a horny consistence, and a 

 iore or less conical shape. At the centre of the top of the 

 :ad is the external opening of the nasal canal, which 

 rminates inferiorly without perforating the palate. The 

 Ills are in the form of fixed sacs, seven on either side, and 

 hich are not furnished with branchial arches. They open 

 ong either side of the neck by seven rounded orifices, 

 iternally these sacs open into a common tube, which 

 feriorly is closed, but superiorly communicates with the 

 outh. Respiration is carried on in these sacs, which can 

 ther receive water by way of the mouth, or directly should 

 ic mouth being employed as a sucker, render taking in 

 ater there impossible. Fins. Two dorsal fins, the pos- 

 :rior being continuous with the caudal. Skin, smooth, 

 id rather tough. No air-bladder. Intestinal canal 

 raight, and possessing a spiral valve. Skeleton cartila- 

 inous and notochordal ; no ribs ; skull not separated 

 om the vertebral column. Colours. Of a greyish or 

 .ive-brown, blotched along the back with black mark- 

 ig, which become irregular ; blotches and spots along 

 ie upper two-thirds of the sides. 



Muller, in 1856, showed that these fishes are subject to a 

 ictamorphosis, the genus Ammocates being in reality its 

 rval form, while it requires at least 3 or 4 years in the 

 nail pride, Petromyzon branchialis, for its complete de- 

 -lopment In the larva the mouth is not circular, while 

 ie lower lip is placed far back and covered by the upper, 

 hich resembles a hood. No teeth of any kind are present, 

 VOL. I.E. i. v 



