Fishes of the Western North Atlantic 



47 



horizontal diameter of eye, about equally spaced, the interspaces about as wide as diameter 

 of eye, the ist gill opening behind eye by a distance about equal to diameter of eye, each 

 gill opening successively lower on side of head from front to rear. Oral disc circular in out- 

 line when attached to a fish or other object, but at other times contracted transversely, leav- 

 ing only a longitudinal fissure open, its diameter when expanded a little greater than 

 greatest thickness of trunk, or about Va as long as head, its margin with 2 to 4 rows of close- 

 set fleshy papillae, the inner rows variously fringed and the outermost row also fringed 

 around posterior part of disc, but smooth around anterior margin. 







Figure 5. A Petromyzon marinus, adult about 450 mm. long, from Merrimack River, N. Hampshire (Harv. 

 Mus. Comp. Zool., No. 35069). B Posterior portion of another specimen of about the same size to illustrate 

 the variation in the length of the interspace between the dorsal fins. C Oral disc of another adult specimen 

 from the Merrimack River (Harv. Mus. Comp. Zool., No. 24975), about natural size. D Central mouth of 

 same with lingual teeth, about 4 x. 



Teeth as described above for genus, those on disc about 1 1 2-1 25 in specimens counted, 

 in curvilinear pattern as illustrated in Fig. 5 C, and marked off in a pavement-like arrange- 

 ment by narrow furrows of the fleshy tissue, although actually their imbedded bases are 

 separated, one from the next, by interspaces of considerable width j teeth varying in sharp- 

 ness in different specimens according to the amount of wear, in extreme cases the supraoral 

 and infraoral dental plates being nearly smooth."*' 



Origin of ist dorsal fin a little posterior to midlength of trunk, its base about V2 

 as long as head, its height a little more than Y^ as long as its base, with nearly straight 

 but sloping margins and broadly rounded apexj interspace between ist and 2nd dorsals 

 varying from very short to about Va as long as base of ist dorsal; 2nd dorsal about twice 

 as long as ist dorsal basally, but similar in shape, its height a little more than Vs its base, 

 and separated from caudal by a definite notch," but continuous with latter at its base; 



57. The genera Bathymyzon and Oceanomyzon were based on specimens in this condition. See footnote 52, p. 45. 



58. Many of the earlier illustrations fail to show this notch, although others do show it 



