28 



are given, but some additional features may be pointed out. The third joint of the antennular 

 peduncle in the female is conspicuously more than half as broad as long and much shorter 

 than first joint. The antennal squama reaches beyond the end of the third joint of the endopod. 

 In both mandibles the cutting edges are furnished with saw-teeth, the edge of the left mandible 

 is nearly transverse, that of the right extremely oblique; a broad, lamellar, distally serrated 

 lacinia mobilis is found on the left mandible but completely wanting on the right ; the setae are 

 spiniform on both mandibles, longer but generally less numerous on the left than on the right 

 mandible ; the molar tubercle is short and very small. — As to the peculiar development in a 

 number of species of the fourth pair or of both third and fourth pairs of pleopods in the male 

 I refer to the general description given above on p. 8 — 9 and to the following descriptions 

 of the species. 



The "Siboga" collection contains not only an enormous quantity of specimens belonging 

 to this genus, but even the number of species is astonishing; in the following I enumerate 13 

 species, 1 1 of which are established as new to science. Hitherto only 7 valid and recognisable 

 species were described, viz. Siriella norvegica G. O. S., 5. Clausii G. O. S., S. jaltensis Czern. 

 (= 5. crassipes G. O. S.), 5. armata H. M.-Edw. and S. frontalis H. M.-Edw. from the European 

 seas, S. Thompsonii H. M.-Edw. from the open Atlantic and the Pacific, and 5. gracilis Dana 

 from the Pacific and the Arafura Sea, while S. Paulsoni Kossm. from the Red Sea, established 

 on a single adult female, may perhaps be recognized when the adult male has been found at 

 the original locality, and 5. pacifica Holmes from California ought to be re-examined. I put 

 this remark because 5. Paulsoni Kossm. and probably S. pacifica Holmes belong to a group 

 of the genus, whose forms must be established on full-grown males, as the females in two or 

 three cases cannot be separated with certainty, while the males show excellent specific characters 

 in the fourth pair of pleopods. All other species established by various authors are either 

 untenable, being mere synonyms, or quite unrecognisable. 



Among the 13 species captured by the "Siboga" only 3 (i of them new) have been taken 

 by other e.xpeditions in the open Ocean, and the majority live probably only in the seas or 

 sounds of the Indian Archipelago. The area explored by the "Siboga" evidently offers excellent 

 conditions for the development of this genus. It may be added that in foot-notes I establish 2 

 new species from Asia not captured by the "Siboga", while a third new species represented 

 by a single "Siboga" specimen too mutilated for description is omitted. 



Key to the Asiatic Species of Siriella. 



I. End of telson with three small spines at the middle and a single pair or 



two pairs of more lateral long spines 2. 



1. End of telson without small spines but with three (four) pairs of very 



long spines 5. dubia n. sp. 



2. Endopod of uropods conspicuously overreaching the exopod 3. 



2. Endopod of uropods at most as long as, generally shorter than, the 



exopod -4- 



