46 Memoir Sears Foundation for Marine Research 



During metamorphosis the eyes become functional, the external segmentation dis- 

 appears, the dorsal fin becomes subdivided, the oral disc and teeth are formed, the bran- 

 chial basket and skull complete their development, the ventral pharyngeal ciliated pit or 

 groove becomes the thyroid gland, the pharynx loses its connection with the alimentary 

 tract, the latter forming a new union with the mouth, while the gall bladder disappears 

 and the bile duct is obliterated." 



Range. Atlantic coasts of Europe and eastern North America; marine but entering 

 fresh water to breed; also landlocked in certain lakes in the northeastern United States. 



Species. It is now generally agreed that the marine Lampreys of this genus represent 

 only a single species (P. marinus hmnzeus, 1758), and the landlocked form of P. marinus 

 (dorsatus, Wilder)" appears to be merely a dwarfed race, without any distinguishing 

 features other than its smaller size. 



Pelromyzon marinus Linnaeus, 1758 



Sea Lamprey, Lake Lamprey, Stone Sucker 



Figure 5 



Study Material. Fifty-one American specimens, up to 710 mm. in length, from East- 

 port, Maine; Exeter, New Hampshire; various localities in Massachusetts and Massachu- 

 setts Bay; Havre de Grace, Maryland (Chesapeake Bay) ; and the Potomac R., including 

 the types of Bathymyzon bairdii Gill, 1 884 (U.S. Nat. Mus., No. 3331 1 ) and Oceanomy- 

 zon wilsoni Fowler, 1907 (Acad. Nat. Sci. Philad., No. 375). Also five Mediterranean 

 specimens from Nice, Messina and Trieste. 



Distinctive Characters. The eel-like appearance of the Lamprey, combined with its 

 circular oral disc surrounding the jawless mouth and the large number of external gill 

 openings, places it at a glance among Atlantic fishes. 



Description. General form eel-like, the trunk about as thick as high anteriorly, but 

 somewhat flattened dorsally, hence ovoid in midsection and strongly compressed toward 

 tail; immature males with a faintly indicated mid-dorsal ridge from about opposite 6th 

 or 7th gill opening to ist dorsal fin, this much more prominent in large maturing males, 

 even while still in salt water; females, at maturity, developing a fin-like crest between 

 anus and caudal fin. 



Head, to last gill opening, a little more thank's of total length; nostril prominent, 

 surrounded by a circular rim, about opposite anterior margin of eye, its distance back from 

 tip of snout about % to % of length of head to last gill opening. Eye approximately cir- 

 cular, its diameter about Vi 6 as great as length of head, its anterior margin a little posterior 

 to posterior edge of oral disc; gill openings round or somewhat oval, about % as long as 



55. For a more extensive account, see Bridge (Camb. Nat. Hist., 7, 1904: 429). It has long been realized that the 

 small Lamprey, repeatedly reported in American waters by early authors as P. nigricans Lesueur, 1818, is merely 

 the young of P. marinus. 



56. In Jordan and Gilbert, Bull. U.S. nat. Mus., 16, 1883: 869. 



