2.5 



b. Mastigopus- Sta ges (figs. 2/ — 2«). — The stages of this species are scarcely discer- 

 nible from those of S. Edwardsiï, which have been described and figured by Kröyer and Bate 

 as .S. oaclatus Kr., and a young stage by Kröyer as S. brachyorrhos Kr. ; besides these stages 

 were mentioned by me in 1896. A large Mastigopus (from Stat. 144) is 10.8 mm. long; the 

 long eye-stalks with the large, very oblique eyes are in the main as in the much younger 

 animal shown in fig. 2/; the rostrum is considerably produced, proportionately about twice as 

 long as in the adult; the terminal joint of third pair of maxillipeds (fig. ini) is divided into 

 4 subjoints, and each of the two distal subjoints shows a feeble transverse line, thus a rudim- 

 entary division into two joints, while the equipment with spines of all 6 subjoints differs widely 

 from what is found in the adult. The abdominal segments without dorsal spines, excepting sixth 

 segment which has a minute spine on the upper terminal angle. The outer margin of the 

 exopod of the uropods ciliated nearly to the base, thus almost as in the adult; telson long and 

 nearly as in the adult. — Fig. 2 / exhibits the carapace with eyes, antennulae and antennal 

 squama of a small specimen measuring (without rostrum) 4.3 mm. length; it is seen that the 

 rostral process is more than one-third as long as the carapace in the median line, and that 

 the supra-ocular and hepatic spines are rather long. The long eye-stalks with the very oblique 

 eyes show the shape peculiar to this form. The antennular peduncles are only two-jointed, the 

 first joint is long, very slender from the end to a little from the base, and this basal part is 

 widened and produced into a triangular, acute process ; the lower flagellum is a minute joint. 

 The abdomen has in this specimen a very distinct spine at the upper hind angle of each of 

 the three posterior segments; the telson is short, only a little longer than in the still younger 

 form mentioned below and similar in shape ; the outer margin of the exopod of the uropods is 

 ciliated in 8 / 9 of its length, and at the end of the short, naked basal part a quite rudimentary 

 spine is seen. — A still younger Mastigoptis is only 3.3 mm. (rostrum not included); its rostrum 

 and the supra-ocular and hepatic spines are still longer than in the preceding larva ; second 

 abdominal segment has a minute dorsal spine considerably before the end, third and fourth 

 segments each a moderately long dorsal spine a little from the end, fifth and sixth segments 

 each a similar spine from the hind angle. The telson is short (fig. 2;/), seen from above shaped 

 in the main as in the Acanthosoma-s,X.a.gz (fig. 2q\ consequently broad from the base to con- 

 siderably beyond the middle, then somewhat narrowed, with each posterior angle produced in 

 a short process terminating in a spine ; the outer margin of the exopod of the uropods (fig. 2 u) 

 is ciliated in scarcely 5 / of its length, and the naked part terminates in a spine. 



c. Acantkosotua- (or Mysis-) S t a g e (figs. 20 — 2q). This stage, which has never been 

 described, is somewhat similar to that of 5. semzmtdus, but differs in various features. The 

 rostrum is about as long as the median line of the carapace, with a number of fine spines. 

 The carapace has the same four pairs of processes as in 5. semzmtdus and besides a process 

 posteriorly in the median line. The first pair of processes, in reality the supra-orbital spines, 

 are very long, more than half as long as the rostrum, curved, with some fine spines. The three 

 other pairs are not half as long as the first pair; the two lateral pairs have lateral branches 

 near the base and more distally a few fine spines. The posterior process originates at the hind 

 margin of the carapace, is directed forwards and a little curved, about half as long as the 



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SIBOGA-EXPEDITIE XXXVIII. 



