7i 



4i. Arachnomysis affinis n. sp. PI. XI, figs. \a — il. 



Stat. 141. August 5. Lat. i°o'.4 S., long. i27°25'.3E. 1950111. Hensen vertical net, from 1500111. 

 depth to surface. 1 specimen, a female witli the marsupium nearly rudimentary. 



Descrip ti on. This species is so closely allied to A. Leuckartii (of which I have 



examined two adult specimens, male and female), that it may be sufficiënt to mention the 

 differences and the telson. The distal joint of the eye-stalks with the eye is scarcely twice as 

 long as broad, thus conspicuously less thick than in A. Leuckartii, in which that joint with 

 the eye is less than half as long again as broad. The front margin of the carapace has 5 

 triangular, short denticles, while in A. Leuckartii they are much or very much longer, slender 

 and spiniform. The four anterior abdominal segments each with a robust, short, acute process 

 at each postero-lateral angle; the five anterior segments each with from 2 to 4 small, acute teeth 

 along the dorsal half of the posterior margin; sixth segment dorsally unarmed; in A. Leuckartii 

 all six segments each with 7 much longer, spiniform, slender processes along the hind margin. 

 Telson a little longer than broad, tapering from before the middle to the truncate end, which 

 is nearly one-third as long as the breadth of the plate-, the postero-lateral angles with minute 

 protuberances, while spines and setae are wanting in the specimen. 



Length of the specimen with the marsupium less than half developed 4.8 mm. 



Remarks. - - A. affinis is very closely allied to A. Leuckartii, but I think that the 

 differences pointed out, which are very conspicuous, cannot be due to age, as my specimen of 

 A. affinis, though immature, shows both pairs of marsupial lamelL-e, and the differences in the 

 dimensions of the eyes and the armature with spines are very striking. 



Tribe 2. Leptoiuysini. 



To this tribe the following genera are referred : Mysidopsis G. O. S., Mysidcis G. O. S., 

 Pseudomysis G. O. S., Batiïymysis Tatt., Leptomysis G. O. S., Uromysis n. gen., Mysidetes Holt & 

 Tatt. and probably the still imperfectly known genus Metamysidella lllig. Though the characters 

 pointed out in the synopsis on p. 12 — 13 between this tribe and the Erythropini may seem 

 somewhat unimportant, I think that the tribe is very natural, as all its genera are allied to 

 each other and rather distant from the genera referred by me to the Erythropini. The shape 

 of the antennal squama and its furniture with setse are very different in the two groups, and 

 Euchcctoincropsis lllig constitutes no real exception. Above on p. 10 I have set fourth good 

 reasons for removing Holmesiella Ortm. from the vicinity of Leptomysis to the Erythropini; 

 it may be added that the endopod, not the exopod, of fourth pair of male pleopods being 

 elongated in Holmesiella points in the same direction. 



The "Siboga" collection contains only a single species, which differs so much trom the 

 forms known that it is necessary to establish a new genus for its reception. 



Uromysis n. gen. 



De scrip ti on. - - General aspect nearly as Mysidetes Holt & Tatt. Carapace anteriorly 

 produced into a moderate frontal plate (PI. XI, figs. 2« and 2/;), posteriorly considerably 



