MARINE SILVER HATCHETFISHES — SCHULTZ 595 



show seven or eight of these pterygiophores, the last two somewhat 

 fused together externally, but all forming a bony blade. 



Another pecularity of the genus is the lack of anal pterygiophores 

 opposite two or three vertebrae, usually beteeen the 9th to 12th caudal 

 vertebrae. The pterygiophores that normally occur opposite these 

 vertebrae are displaced anteriorly and posteriorly, where they are 

 crowded between adjoining vertebrae. 



In certain groups of photophores the organs in the post larvae 

 increase in number with increase in length up to a certain size, after 

 which the full complement of light organs are formed. For example in 

 Argyropelecus hemigymnus, the relationship of number of organs to 

 standard length is: 



These data indicate for A. hemigymnus that the full complement 

 of photophores for the preanal, anal, and subcaudal groups is not 

 reached until a standard length of about 10 mm. is attained. In 

 A. aculeatus the anal photophores reach six in number at about 12 mm. 

 in length. 



Tables 1-3 give tho counts and measurements that were made for 

 certain species and subspecies of Argyropelecus. 



Key to Species of Argypropelecus 



la. Supra-abdominal, preanal, anal, and subcaudal groups of photophores near- 

 ly in a straight and almost continuous line; 2 short postabdominal spines 

 (occasionally lacking) about equal length, the acute angle between them 

 about 10 to 15 degrees; lower preopercular spine directed downward and 

 curving outward and forward; upper preopercular spine hooked out- 

 ward and usually forward, not extending to bony edge of preopercle. 

 2a. No post orbital spine; dorsal blade short, length of exposed part of last 

 spine above pigmented area contained about 2.2 to 3.3 times in base of 

 soft dorsal; origin of base of soft dorsal on same level as pigmented base 

 of dorsal blade; palatine teeth present, moderately strong. 



