METHODS 



Except as noted, methods of measuring and counting followed those suggested by Hubbs 

 and Lagler (1947). All measurements were made with dial calipers and recorded to the nearest 

 tenth of a millimeter. All lengths refer to standard length unless otherwise stated. The count 

 of dorsal and anal fin rays did not include the anteriormost, often difficult to perceive, small 

 ray; the last ray of these fins was bifurcate to the base and was counted as one. The tiny, often 

 nearly invisible lower rays of the pectoral fins were counted while immersed in water. Only the 

 principal gill rakers were counted (on the upper and lower limbs of the outer arch only), except 

 for the genus Gonichthys, in which the rakers became progressively shorter on the lower limb 

 without the usual sudden decrease in size (to "nubs") anteriorly. Both sides were counted for 

 pectoral rays and for anal ( AO) photophores. Also, if only a few specimens were available, both 

 sides were counted for gill rakers. In the tabular data on numbers of gill rakers, the central 

 raker (at the juncture of the upper and lower limbs) was included in the count for lower rakers. 



The depth of head was measured vertically through the end of the upper jaw, rather than 

 vertically from the occiput. The distance the upper jaw extended beyond the orbit was derived 

 by subtracting from the length of the upper jaw the distance from the tip of the upper jaw to the 

 posteriormost margin of the orbit. The remainder was calculated as percent of upper jaw 

 extending behind the orbit. This method yields a more precise value than the commonly used 

 visual determination of a vertical from the rear margin of the orbit to the upper jaw, or a 

 perpendicular from upper jaw to there. All measures of distance from tip of snout (upper jaw) to 

 fins were made to origins of the fins, except for the adipose fin; in this case the end of the base of 

 the fin, rather than the origin, was used as it afforded a more precise point than the often 

 difficult to perceive (and often arbitrarily selected) origin of the gently rising "ramp" of this 

 base. Thus, the values for "preadipose length" given in the various tables may be slightly 

 greater than those given by other authors. 



Unless otherwise stated, all values for body proportions, given in the various tables, are 

 expressed as thousandths of standard length. 



The location and terminology of the photophores and other luminous organs of head and 

 body used in the identification of myctophid fishes are shown in Figs. 1, 78, and 84. In general. 



Vn So Bu Op PLO 



Supracaudal Gland 



AOp \ Pre 



Infracaudal Gland 



AOa 



Fig. 1— Diagram of a myctophid fish showing the location and terminology of commonly occurring photophores. No one 



species will bear all the photophores shown. 



