41 



excepting the genital plate. In these females the plate (fig. 2 a) is less broad and considerably 

 shorter than in the typical A. dispar, and it reaches only to or a little beyond the transverse 

 furrow; its posterior margin is somewhat concave or nearly straight, and. the keels on its lower 

 surface are feeble. Length of a large specimen 22 mm. — Having no males I am unable to 

 settle whether these females are only a variety of A. dispar or belong to a separate species. 



Remarks. — A. dispar is instantly separated from all forms known to me, excepting 

 A. cJiinensis n. sp., in having the ciliated part of the outer margin of the exopod of the uropods 

 almost or fully as long as the glabrous part. Judging from the petasma it is allied to A. japo- 

 niais Kishinoye, but as the Japanese author, who had a rich material of his form, does not 

 mention any sexual difference in the length of third joint of the antennular peduncles, it is 

 impossible to refer the typical A. dispar to his form, because the third joint mentioned is so 

 very much elongated in the male A. dispar, that it seems to be impossible that Kishinoye 

 could overlook such a sexual difference. Perhaps the females described as a possible variety 

 belong to the Japanese form. 



4. Acetes chinensis n. sp. PI. IV, figs. 3a — ^b. 



Not taken by the "Siboga", but the Copenhagen Museum possesses females from the 

 following localities. 



Lat. 33°io'N., long. 129° 18' E. 40 fathoms. Capt. Suenson, 17 Sept. 1897. 5 females. 

 Formosa Channel, 25 fathoms. Capt. SuENSON, 23 May 1S97. ' female. 



Female. — It agrees with A. dispar in the antennulae, the coxae and trochanteres of 

 third pair of legs and the exopod of the uropods (fig. ib), but differs sharply in the shape of 

 the genital plate. Inside the small rounded plate projecting from the proximal inner corner of 

 each coxa of third legs a minute protuberance is found. Seen from the side the posterior part 

 of the genital plate is much thicker than in A. dispar \ seen from below (fig. 3^) the plate 

 overreaches somewhat the furrow between the two last thoracic segments; from its broad base 

 its lateral margins converge strongly backwards and curve finally so much inwards, that the 

 posterior margin is their direct continuation; the latter margin is incised at the middle; the 

 lower side of the plate has a broad, longitudinal excavation which especially in its posterior half 

 is deep, so that each lateral part of the plate looks as a thick, oblong protuberance. 



Length 22 — 32 mm. 



Remarks. — The genital plate differs so much from that in A. dispar that the animals 

 must belong to a separate species, possibly A. japonicns Kishinoye, and it can not be difficult 

 to recognize the species with certainty. 



5. Acetes serrti/atns Kroyer. PI. IV, figs. 4^ — 4/;. 



1859. Sergestt's serrulatiis Kroyer, Kgl. D. Vid. Selsk. Skrifter, Math.-naturv. Afdeling IV, 2, 

 p. 268, Tab. IV, fig. 12, a— g. 



The "Siboga" has not secured this species, but the Copenhagen Museum possesses it 

 from 3 places, 2 of which within the "Siboga" area. 



SIBOGA-EXPEDrriE XXXVllI. 6 



