Fishes of the Western North. Atlantic 103 



12 a. Teeth enormous, conspicuous even when mouth 

 is closed; first dorsal ray greatly prolonged. 



Chauliodontidae in part, Part 4.*' 

 :2b. Teeth small to moderate in size; first dorsal ray 

 not greatly prolonged. 



13 a. Upper edge of mouth formed by both max- 

 illaries and premaxillaries; upper jaw teeth 

 extending outside lower jaw when mouth is 

 closed; photophores generally present on 

 branchiostegal membrane. 



Gonostomatidae in part. Part 4.^' 

 13 b. Upper edge of mouth formed by premaxil- 

 laries only; upper jaw teeth contained within 

 mouth; no photophores on branchiostegal 

 membranes. 



14 a. Distance from pelvics to anal origin not 

 more than twice the length of eye. 



Myctophidae in part, Part 5.*' 

 14 b. Distance from pelvics to anal origin at 

 least 3 times longer than eye. 



Neoscopelidae in part. Part 5.^' 

 1 1 b. No dorsal adipose fin. 



15a. Body with at least 20 longitudinal rows of scales; 

 mouth not widely distensible; gape not extending 

 past eye; teeth small. 



Alepocephalidae in part, Part 3, p. 250.'" 

 15b. Body without scales; mouth enormously disten- 

 sible; gape extending beyond eye by a distance 

 3 or more times the length of eye; teeth large and 

 conspicuous. Malacosteidae in part, Part 4.^^ 



Key D. Eyes either tubular (teleoscopic), or with pupil above ccnter and ca- 

 pable OF being directed upward, or with eye situated at the tip of a 



SLENDER stalk. 



I a. Eyes not at tips of slender stalks. 



2a. Lower lobe of caudal much longer than upper lobe; gill openings minute; 

 base of pectorals wholly above gill openings. Giganturidae, Part 4. 



56. See also Kev C, 4 b. 



57. Exceptions: in Ickthyococcus the upper jaw is formed bv the maxillaries alone, and in Triplophos it is ahnost entirely 

 bordered by the premaxillaries. 



58. See also Key D, i b. 59. See also Key B, 15 a. 

 60. See also Key A, 6a; Key A, 11 a. 61. Sec also Key C, 7 b. 



