600 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
opposite direction. This compensatory variation is not due solely to the shifting of the photophore 
from the anterior to the posterior group, or in the opposite direction, for tlje supra-anals maintain a 
constant relation to the last antero-anal, whatever the number. 
Specimens were taken at the following stations: Nos. 3878, south of Lanai; 3926, west of Oahu; 
3927, west of Niihau; 3930, near Laysan Island; 3980, south of Oahu; 4009, west of Oahu; 4011, west 
of Oahu, and 4145, west of Niihau; all at the surface. 
Scopelus spinosus Steindachner, Iehthy. Notizen, V, 1867, 11 (author’s reprint) , pi. 3, figs. 4-4a. China. 
Scopelus ( Dasyscopelus ) spinosus Liitken, Spolia Atlantica, Scopelini, 1892, p. 239, pi. 1, figs. 1-2. Tropical Atlantic; Maldon 
Island, S. Pacific. 
Dasyscopelus pristilepis Gilbert & Cramer. 
One of the most abundant species at the surface, where young and half-grown specimens were 
frequently taken in the tow-net. One adult was found in the stomach of a dolphin, in the Honolulu 
market. 
D. pristilepis agrees with D. asper (Richardson), the type of the genus, and differs from D. spinosus in 
the greatly enlarged thickened scales of the lateral line. The depth of these scales, when fully exposed, 
exceeds their distance from the base of the dorsal fin. In spinosus, the scales of the lateral line are 
very little if at all enlarged. In both species, the scales of the lateral line are overlapped and almost 
wholly concealed by the series above and below them, and the tubes of the lateral line are strongly 
developed, forming keel-like projections. D. asper differs from pristilepis in the presence of a large 
preocular photophore, extending from middle of eye forward to around nostrils; furthermore, the anal 
spots are 10+4, and the 2 caudal photophores are widely separated. 
The number and distribution of the luminous spots in D. pristilepis have been tabulated in the 94 
specimens of the collection. No variation was found, except in the anterior and posterior anals. 
These have for their normal formula 7 for the anterior group and 4 for the posterior, but the anterior 
may vary from 6 to 8 and the posterior from 3 to 5. A plus variation in the anterior group is more 
frequently connected with a minus variation in the associated posterior group, the 2 varying in a 
compensatory manner. For this reason, the variation in the total number of the anal spots found on 
one side of any individual is no greater than the total variation found in each group separately, and 
comprises only the numbers 10, 11, and 12. The combinations 6+3 and 8+5, although within the 
ascertained range of variation of anterior and posterior groups taken separately, do not occur in our 
material. 
The 2 sides of a fish do not always agree in the number and arrangement of the spots. We must 
therefore tabulate each side separately, giving thus for consideration, with our material, 188 cases. Of 
these, we find in the anterior group: 6 photophores in 11 cases, 7 photophores in 160 cases, 8 photo- 
phores in 17 cases. In the posterior group: 3 photophores in 21 cases, 4 photophores in 157 cases, 5 
photophores in 10 cases. 
As already stated, the size of the 2 associated groups is not purely a matter of chance. Thus when 
the anterior group contains 6 photophores, only the combinations 6 + 4 and 6 + 5 are found, as follows: 
6 + 4 in 5 cases, 6 + 5 in 6 cases. When the anterior series contains 7, it may be associated with 3, 4 or 
5 in the posterior series, as follows: 7 + 3 in 9 cases, 7 + 4 in 147 cases, 7 + 5 in 4 cases. When the 
anterior series contains 8, only the combinations 8 + 3 and 8 + 4 are found, as follows: 8 + 3 in 12 cases, 
8 + 4 in 5 cases. 
- Opposite sides of the same fish may vary independently, as appears from the occurrence of the 
following combinations: 7 + 3 occurs bilaterally in 2 specimens, unilaterally in 5; '7v~ 4 occurs bilat- 
erally in 66 specimens, unilaterally in 15; 7 + 5 occurs bilaterally in 1 specimen, unilaterally in 2; 
6 + 4 occurs bilaterally in 1 specimen, unilaterally in 3; 6 + 5 occurs bilaterally in 2 specimens, unilat- 
erally in 2; 8 + 3 occurs bilaterally in 4 specimens, unilaterally in 4; 8 + 4 occurs bilaterally in 1 
specimen, unilaterally in 3. In deviations from the mode (7 + 4) there thus appears a distinct 
tendency toward a symmetrical variation. The chance nature of the association of groups on opposite 
sides of the same individual is evident from a consideration of the 15 specimens, noted above, in which 
7 + 4 occurs unilaterally: the combination 7 + 4 and 7 + 3 occurs in 5 specimens; 7 + 4 and 7 + 5 in 1 
specimen; 7 + 4 and 6 + 4 in 3 specimens; 7 + 4 and 6 + 5 in 2 specimens; 7 + 4 and 8 + 3 in 2 speci- 
mens; 7 + 4 and 8 + 4 in 2 specimens. 
A minute photophore surrounded by a black ring is present on the lower anterior orbital margin. 
In the adult specimen only, 2 scales on lower edge of caudal peduncle cover luminous spots. 
