ió 



1 7 mm. long. The eyes are distinctly smaller with their stalks proportionately longer, and the 

 rostrum is less produced than in the adults, but the most interesting difference is that fewer 

 photophores are found. These organs are well developed on the lower side of the thorax, but 

 on each side of the carapace only one organ exists, while the antennal squama, which is easily 

 examined, has only two organs ; the more special, very difficult search for photophores has not 

 been undertaken. — One of the largest specimens with the thick outer layer of the eyes 

 yellowish, is 13 mm. long; it is a transition-stage between the real Mastigopus and the young 

 specimen with black eyes just mentioned. It differs in having the antennular peduncles (fig. 42) 

 conspicuously less robust and the eyes considerably smaller with their stalks longer-, the rostrum 

 has a small, acute angle above, while its distal part is slender, acute-, the two posterior pairs 

 of thoracic legs are less developed, and sixth abdominal segment has its posterior upper angle 

 produced into a very small spine. Several well developed photophores are found on the lower 

 side of the thorax; second maxilliped has at least four organs, and an organ is found on the 

 lower side of the eye-stalks near the eye, but no organ could be discovered on third maxil- 

 lipeds, on the thoracic legs, the sides of the carapace and above all on the lower side of the 

 antennal squamse. — Figs. \l an d 4^' represent respectively the anterior part of the body and 

 the exopod of left uropod of a real Mastigopus measuring 12.3 mm. in length. It is seen that 

 the rostrum (<?.) is small with a small upper tooth, while the eye-stalks are long, so that the 

 eyes, which are considerably larger than in the stage just mentioned, are situated above the 

 articulation between first and second joint of the antennular peduncle; this peduncle is as usual 

 in Mastigoptis-ioxm?, rather slender; fifth and sixth abdominal segments each with a small spine 

 on the upper posterior angle ; the ciliated part of the outer margin of the exopod of the uropod 

 (as usual in this sub-group of Sergestes) distinctly longer in proportion to the naked part than 

 in the adult ; finally it was impossible to find any photophores on the ventral side of the thorax 

 or on second maxilliped, and they are probably entirely wanting. 



Remarks. The differences between S. Ckalletigeri, S. splendens n. sp. (from the Atlantic) 

 and 5. ftilgens are mentioned in the description, with remarks, of the last-named form. 



Distribution. — The 'Challenger' specimen was taken at "Lat. i9 a/.35S., long. 

 i79°4i'.50 E.; off Matuku, Fiji Islands; depth 315 fathoms". Kemp's specimens were gathered 

 in the western part of the Indian Ocean, viz. at lat. io°27'S., long. 5i°i7'E., 800 — o and 

 1000 — o fathoms, and "6 miles N. N.W. of Desroches Atoll", 200 to o fathoms. 



Sergestes sp. PI. I, fig. 5 a. 



Stat. 100. June 29. Lat. 6°n'N., long. 120 37'. $ E. 450 m. Dredge. 1 adult male. 



The single male, which measures 32.5 mm. in length, cannot belong to 6". Challengeri\ 

 it is very closely allied to this species, agreeing with it in the petasma and every other 

 particular, but the third joint of the antennular peduncle and the lower flagellum are very 

 different. The distal part of that third joint (fig. 5a) is slightly expanded downwards, but its 

 lower part is produced considerably forwards, with its terminal inferior corner cut off obliquely 

 and bearing a long and extremely thick, acute seta or spine. The lower flagellum differs 



