fff^n w s* 



the fourth, and in 5. anoinala n. sp. besides the third, pair of pleopods differ from the other 

 pairs. In some species, as S. conformalis n. sp., S. distifiguenda n. sp. and S. ccqiiiremis n. sp., 

 the endopod is distinctly longer than the exopod with its four or three most distal setae naked 

 and at least the two terminal setee stronger than the plumose more proximal setae. In S. media 

 n. sp., 5. inornata n. sp., 5. pbmticauda n. sp. and S. serrata n. sp. both rami of fourth pair 

 are equal in length, but both have the distal or only the terminal setae peculiarly developed, 

 at least two among them being very strong and partly or quite naked. In S. anomala n. sp. 

 fourth pair of pleopods show nearly the same structure as in .V. aquiremis n. sp., but besides the 

 third pair have the endopod somewhat longer than the exopod, with the penultimate joint very 

 elongated and the terminal setae of the last joint very broad, peculiarly shaped, oblique. Thus 

 the eight species enumerated differ sharply from S. Thompsonii H. M.-Edw., 5. gracilis Dana, 

 S. qiiadrispinosa n. sp., 5. nodosa n. sp., 5. vulgaris n. sp. and S. affinis n. sp. in the structure 

 of the pleopods named, and besides it is astonishing to find such sexual differences between 

 the males of otherwise closely allied species, in a couple of cases even so nearly related that I 

 have been unable to find trustworthy differences between their females. In the European species 

 S. norvegica G. O. S., S. Clausii G. O. S. and S. jaltensis Czern., which are rather similar to 

 5". ceqtdremis n. sp. in the spinulation of the distal part of the telson, the pleopods of fourth 

 or third pair have both rami equal in length and none of their setae peculiarly developed. 



In the interesting genus Rhopalophthalnius Illig, which I take as the type of a new sub- 

 family, all pleopods are well developed but the exopod of second pair is exceedingly elongated. 

 In the Boreomysinae the pleopods are well developed, but the exopods of second and thirds 

 pairs are somewhat or considerably elongated (sometimes the second more so than the third, 

 sometimes vice versa) and the setae on the distal joints of third exopod or of both second and 

 third exopods are reduced in length. 



In the subfamily Gastrosaccinae, comprising Anchialina Norm. (= AncJiialiis Kr.), Par- 

 anchialina n. gen. (type: Anchialus angustus G. O. S.), Arckisomysis Czern., Callofuysis Wo\m&s., 

 Gastrosaccus Norm. {Chlamydopleon Ortm., Haplostylis Kossm.), and Pseudanchialina n. gen. 

 (type : Anchialus pusillus G. O. S.), the e.xopod of third pair is always conspicuously or even 

 extremelj- elongated, and the pleopods show several interesting peculiarities as to the degree of 

 their development. In Anchialitia and Paranchialina the exopod of third pair is less or more 

 elongated and frequently with the distal part ver)- peculiarly developed, though very different 

 in various species (comp. this exopod in A. typica Kr., PL VII, fig. 2z, with that in A. grossa 

 n. sp., PI. VIII, fig. i6)\ the endopod and the other pleopods are well developed, normal. Of 

 Gastrosaccus Norm, (including Haplostylis Kossm.) I have examined eight species, all similar in 

 aspect and allied to each other in most particulars excepting the degree of development of the 

 pleopods : the exopod of third pair is always very, sometimes exceedingly, elongated, but the 

 endopod is sometimes normally developed, sometimes rudimentary or scarcely discernible or 

 perhaps wanting ; the rami of second pair are either normal or the endopod is much reduced ; 

 fourth and fifth pairs are always reduced in size, but sometimes the exopod is normal in shape, 

 the endopod unjointed [G. sanctus v. Ben.), sometimes both rami are unjointed {G. indicjis n. sp., 

 PI. VIII, figs. 2tn — 2;z), sometimes the exopod is quite rudimentar}' while the endopod is a simple 



SIBOGA-EXPEDITIE XXXVII. 



