BRITISH FRESHWATER FISHES 



Lamprey, have been described as a distinct genus and 

 species under the name Ammoccetes branchialis. 



THE SEA LAMPREY (Petromyzon marinus) is dis- 

 tinguished from the others by its dentition. The suck- 

 ing disc is covered with conical teeth arranged in 

 oblique radiating series, four inner teeth on each 





FIG. i. Suctorial discs of Sea Lamprey (a) and Lampern (b). 

 s. supra-oral lamina ; /. anterior lingual lamina ; i. infra-oral lamina. 



side being enlarged and bicuspid ; the supra-oral 

 lamina is narrow and bicuspid, the infra-oral lamina 

 has seven to nine cusps, and the anterior lingual 

 lamina bears two curved denticulated ridges 

 separated by a median longitudinal groove. The 

 first dorsal fin is separated from the second by an 

 interspace, the second from the caudal only by a 

 notch. The colour is grey, yellow, or green, marbled 

 or spotted with olive, brown, or black. 



The Sea Lamprey attains a length of more than 



