Jordafi and Evennann. — P'ishcs of North America. 



no pelvic elements, no ribs. Gills in the form of fixed sacs, without 

 branchial arches, 6 or more in number on each side. Nostril single, 

 median. Month subinferior, suctorial, more or less circular. Heart with- 

 out arterial bulb. Alimentary canal straight, simple, without cwcal ap- 

 pendages, pancreas, orspleen. Generative outlet peritoneal. Vertical fins 

 with feeble rays, usually continuous around the tail. Naked, eel-shaped 

 animals, inhabiting cool waters, both fresh and salt. They undergo a 

 metamorphosis, the young being often quite unlike the adult. (Subclass 

 Cyclostomi, Giinther, Cat., viir, 1870, 499-512.) (juapaimov, pouch; 

 PlJ'hxi"-, gills.) 



Orders of Marsipobranchii. 



a. Nasal tube tUict-like, with cartilaginous rings, penetrating the palate; gill openings remote 

 from the head, opening directly into tlie pharynx; no eyes. HYPEEOTnETi, B. 



««. Nasal duct a hlind sac, not penetrating the palate; gill openings close behind the head, 

 communicating with a common branchial passage which opens directly into the pliar- 

 ynx; eyes well developed in the adult. HypEROARTii, C. 



Order B. HYPEROTRETI.* 



(The Hagfishes.) 



Nostril tube-like, with cartilaginous rings, penetrating the palate, its 

 position at the extremity of the head, over the mouth; snout with 8 

 barbels; mouth without lips; 1 median tooth on the palate and 2 comb- 

 like series of teeth on the tongue. Branchial apertures at a great distance 

 from the head; a series of mucous sacs along each side of the abdomen. 

 Intestine without spiral valve. Eggs large, w^ith a horny case i^rovided 

 with threads for adhesion. Marine lamprey-like animals, burrowing into 

 the flesh of fishes, on which thcj' feed. They may be referred to 2 families, 

 difi'ering mainly in the structure of the gill openings. {vTzepilia, palate; 

 '"<"/'"?) perforate). 



n. Branchial apertures G to 14 on each side, each leading by a duct to a branchial sac. 



HEPTATREMin.E, II. 



.711. Branchial apertures single on each side, from which diverge ducts to 6 branchial sacs. 



Myxinid.v, in. 



Family II. HEPTATREMIDJE. 



(The Borkrs.) 



This family differs from the Mi/xinido' chiefly in the structure of the 

 branchial apparatus, there being 6 to 14 sacs on each side which receive 

 water directly from the cpsophagus, as in Mijxiue, but the emptying 

 ducts, instead of passing backward and downward to a common external 

 opening, as in Myxinc, pass directly through the wall of the body, so that 

 there are as many external openings as there are gill sacs. Species about 

 5, referable to 2 genera, inhabiting the colder parts of the Pacific, their 



* For a general account of our species of Iliiuerotreli, see Putnam, Proc. Bost. Soc. Nat. Hist., 

 1873. i Jf . . 



