TiOO BULLETIN OF THE UNITED STATES FISH COMMISSION. 



opposite (lirt'ction. 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 the supra-anals maintain a 

 constant relation to the last antero-anal, whatever the luniil.ier. 



Specimens were taken at the following stations: Nos. .SS7S, soutli of Lanai; 3926, west of ()ahu; 

 3927, west of Niihau; 3930, near Laysan Island; 39S0, soutli of Oahn; 4009, west of Oahu; 4011, west 

 of Oahu, and 4145, west of Niihau; all at the surface. 



Si)ji' Ins aphioi^ilii i^l<yini\whni'r. Iclahy. NoIizLMi. V, ISt'.T. U (:iuthnr's rfpriiit), pi. 3. figrs. 4-4n. f'hinu. 

 Srojutny {Ditsii/irojitUua) Kpinostts Liitken. Spolirt Athintica, Sriijiclini, IS'.vj. p. 'J3'.>, pi, 1, tis.«. 1-2. Tropical Atlantk': MiOdon 

 Lsland, S. I'aciflc. 



Dasyscopelus pristilepis <iilhrit A Cramer. 



OiUMif the most aliundant species at the surface, where young and half-grown specimens were 

 treiiueiilly taken in the tow-net. One adult was foninl in the stomach of a dolphin, in the Honolulu 

 market. 



I), jiriittlli'pis agrees with D. d.ipi'r ( Richardson ) , the ty jie i >f the genus, and differs from D. f^jAnoms in 

 the greatly enlarged thickened scales of the lateral line. The dejith of these scales, when fully exposed, 

 exceeds their distance from the base of the dorsal fin. In Hjiinoxus, 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 tulies of the lateral line are strongly 

 deN'eloped, forming keel-like jirojections. T>. axj)cr fliffers from prhlUepix in the presence of a large 

 preocular photo])hore, 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. pristilfpig have been tabulated in the 94 

 specimens of the collection. No variation was found, except in the anterior and po.'^terior 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 [losterior 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 oidy the numbers 10, 11, and 12. The coniliinations 6+3 and 8+5, although within the 

 ascertaineil range of variation of anterior and posterior grou]>s 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 fiml in the anteri<ir group: 6 photophores in 11 cases, 7 photophores in 160 cases, S photo- 

 phores in 17 cases. In the |iosterior group: 3 jihotophores in 2! ca.'^es, 4 photophores in 157 cases, 5 

 photojihores in 10 cases. 



As already statc<l, the size of the 2 associated groups is not purely a matter of chance. Tims 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 jiosterior series, as follows; 7 ~ 3 in 9 cases, 7 -■ 4 in !47 ca.ses, 7 + 5 in 4 cases. When the 

 anterior series contains 8, only the coniliinations 8 t 3 and 8 -j- 4 are ftmnd, 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 coniliinations: 7 + 3 occurs bilaterally in 2 siiecimens, unilaterally in 5; 7 + 4 occurs bilat- 

 erally ill 66 specim ns, 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 niod(^(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 S --- 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 orViital margin. 

 In the adult. specimen only, 2 scales on lower edge of caudal peduncle cover luminous spots. 



