17 



extremely from the clasping org-an in the male 5. Challengeri or 5. ftilgens, as it is more 

 similar to the flagellum in a female, from which it differs only in having the second joint 

 (fig. 5«) longer and above at the end produced into a small, obtuse process. Third joint of the 

 peduncle and the proximal joint of the lower flagellum are rather similar to the same parts in 

 the Atlantic form 5'. splendetis, through showing differences in two or three small particulars; 

 the petasma agrees with that in 5. Challengeri, and differs from 5. splendens in a few small 

 features. The specimen is mentioned here, as future investigators with a richer material of these 

 luminous forms of Sergestes ought to keep outlook in order to solve the difficulties. 



6. Sergestes fulgetis n. sp. PL I, figs, da — bg. 



Stat. 312. Febr. 14. Lat. 8° 19' S., long. ii7°4i'E. Saleh-bay, North coast of Sumbawa. 274 m. 

 Trawl. 22 specimens, 16 of which are adult males. 



This species is so closely allied to S. Challengeri that a half-grown female can scarcely 

 with absolute certainty be distinguished from an adult female of the last-named species excepting 

 by the fact, that in the latter the antepenultimate thoracic segment has its lower surface between 

 the coxae adorned with keels and protuberances, which are not found in the immature S. fulgens. 



S. fulge7is is much larger and looks proportionately more robust than 5. Challengeri. 

 The rostrum (fig. 6«) is distinctly longer than deep, thus somewhat more produced than in 

 5. Challefigeri. The eyes are seemingly a little larger in proportion to first joint of the anten- 

 nular peduncles, and a little longer in proportion to their stalks than in S. Challengeri. The 

 terminal joint of third maxillipeds (fig. 6d) is as in the last-named species divided into four 

 sub-joints, each of the two distal conspicuously longer than the second and especially than the 

 first, but third sub-joint is sometimes, but scarcely always, more or less distinctly subdivided 

 into two joints, as shown in the figure. By far the best character between 5. fulgens and the 

 other luminous forms is the shape of third joint in the antennular peduncle in the male. This 

 joint (fig. db) is extremely characteristic and shows no variation worth mentioning in the numerous 

 adult males examined. The distal third of the joint is on the lower side produced strongly 

 downwards, somewhat forwards and a little inwards as a plate which has a very deep and 

 rounded terminal incision so that- both the lower anterior and the posterior corner of the plate 

 have each a long process; the anterior process is straight and considerably longer than the 

 posterior, a little curved process, and both processes have the end obtuse. The clasping organ 

 of the lower flagellum (fig. be) is shaped nearly as in 6". Challengeri, but the curious setae along 

 the upper margin of second joint are about sixteen, and the most proximal setae are longer, 

 the most distal ones thicker than in 5. Challengeri. — The carapace has on each side either 

 6 or 5 photophores in a row. 



The petasma (figs. 6e — 6^) is so similar to that in 5. Cliallengeri described above that 

 some remarks may be sufficient. The distal part of processus uncifer (/«.) is conspicuously 

 expanded inwards. The hooks on the posterior side of lobus armatus [la) near its outer margin 

 are smaller and somewhat more numerous than in S. Challengeri. Lobus connectens (/^.) has 

 the distal margin less deeply curved, the outer lobe more narrow, the inner broader than in 



SIBOGA-EXPEDITIE XXXVIII. -i 



