GILBERT: FISHES OF THE SUBGENUS LUXILUS


 METHODS OF COUNTING AND MEASURING

 To reduce sample bias usually no more than 10 specimens were
counted from a single series, except in lots from certain critical or
poorly collected areas, where larger numbers were used. As certain
relative body proportions change with increase in size, body measure-
ments were made only on specimens falling within certain size ranges
in each species. For the larger forms (N. cornutus, N. albeolus, N.
chrysocephalus, and N. coccogenis) specimens measuring approxi-
mately 60 to 80 mm in standard length were used; for the smaller
species (N. zonistius, N. cerasinus, N. zonatus, and N. pilsbryi) the
limits were 55 and 75 mm.
 Counts and measurements were taken as outlined by Hubbs and
Lagler (1947: 8-15) except that the mouth gape was determined by
the transverse distance between the posterior angles of the mouth,
instead of the greatest transverse distance across it. To eliminate
difficulties in counting fine-scaled species, a new method was de-
vised for taking scale counts on the anterior dorsal part of the body.
The usual predorsal scale count on the dorsal midline directly in front
of the dorsal fin is entirely satisfactory for coarse-scaled species, but
overlaps and irregularities in fine-scaled forms make accurate deter-
minations difficult. The scale rows along the side of the body are
more regular than the predorsal scales, and provide a more accurate
and effective assessment of differences in scale size among popula-
tions.
 Anterior dorsal-lateral scale counts were made along the longi-
tudinal row of scales lying approximately three-fourths of the distance
from the lateral line to the mid-dorsal line. This varied from the
third to the sixth row above the lateral line, depending on the size
of the scales. The scales were counted from a point directly under
the origin of the dorsal fin forward to their termination. The sum
of this count and the body circumferential scale count is of great
value in interpreting differences between the various species, par-
ticularly those in the N. cornutus species group.
 Scale counts for both the circumferential and the caudal peduncle
series are usually expressed as total numbers, but may also be writ-
ten to indicate the relative disposition of scales above and below
the lateral line. Thus a circumferential count written as 14-2-10
signifies 14 scales between and above and 10 scales between and
below the lateral lines on each side of the body.


1964