724 CONTRIBUTIONS TO NORTH AMERICAN ICHTHYOLOGY IV. 



the isthmus; ventral fins thoracic, close together, imperfect, I, 2 or I, 3; 

 spinons dorsal small, sometimes absent; anal short, similar to soft dor- 

 sal, without spines; caudal narrow, few-rayed; pectorals entire, with 

 broad base, the rays mostly simple; pyloric coeca few; air-bladder 

 none. Small fishes, chiefly of the Arctic Seas. Genera about 10; spe- 

 cies about 16. They feed chiefly on Crustacea, and are often found at 



considerable depths. 

 (Triglida;, group Cataphracti pt. Giinther, ii, 211-216.) 



a. Spinous dorsal obsolete ; gill-membranes free from the isthmus. (Aspidophoroidina. ) 



ASPIDOPHOROIDES, 381. 



an. Spinous dorsal present. 



b. Gill-membranes free from the isthmns; lower jaw projecting, 

 c. Body extremely elongate; snout forming a tube; chin with a single long 



barbel SIPHAGOXUS, 382. 



cc. Body fusiform, less elongate; snout not forming a tube; chin without barbel. 



BRACHYOPSIS, 383. 



bb. Gill-membranes united to the isthmus, lower jaw included. 

 d. Bony plates of body without spines. 



f. Vomeriue teeth none; no occipital pit AGONUS, 384. 



ee. Vomeriue teeth present ; a deep pit at the occiput BOTHIIAGON us, 385. 



dd. Bony plates of body ending in spines. 



/. Vomerine teeth present ODONTOPYXIS, 386. 



ff. Vomerine teeth none PODOTHECUS, 387. 



31. ASPIDOPHOROIDES Lacpede. 

 (Anoplagomis Gill.) 



(LacrpJ-dr, Hist. Nat. Poiss. iii, 228, 1802: type Aspidophoroides tranquebar Lac. = Cofua 

 monopterygiue Bloch. ) 



Body very long and slender, subterete, octangular, tapering into a 

 very long six-sided tail. Head slender, short, with large eye; mouth 

 small, terminal ; jaws and vomer with villiform teeth. Dorsal fin 

 single, without spines, very small, inserted nearly opposite the still 

 smaller anal; other fins small; bony plates of body keeled, without 

 spines; gill-membranes broadly united, free from the isthmus. (da-Is, 

 shield; (,'"'/' - w j to bear; er^r, appearance.) 



a. N.isal spines very strong. 



11OO. A. moiiopK c > :;iiis (Bloch) Ston-r. 



P.roxvuish, obscurely banded with darker; pectorals, dorsal, and cau- 

 dal mottled or barred. Head triangular, much narrowed anteriorly; 

 nasal spines very large, diverging, inserted near tip of snout; no other 

 spines anywhere; eyes very large, longer than snout; supraocular 

 ridges very high; a ridge extending backward from eye along tern- 



