31,2 PEECT SLADEN TEUST EXPEDITION. 



lio-ht- coloured holothurians, Holothuria maculata, Brandt, and a Avliite species of 

 Actinopyga. In these last cases the polynoid is associated with the same species of 

 crab, as a fellow-commensal, which has undergone an identical colour-change. 



On a number of specimens examined I was able to confirm Willey's statement as 

 to the extraordinary insertion of the elytra on the ])osterior segments. The numbers 

 of their segments were 2, 4, 5, 7,-23, 26, 29, 32, 35, 36, 38, 39, 41, 43, 45, and the 

 distribution is quite invariable. 



Locality. This species occurs commonly throughout the islands of the Indian Ocean 



and at Zanzibar. 



Geuus LEPIDASTHENIA. 



Included in this well-defined genus are all Polynoids with an elongated body and 

 minute elytra, leaving the greater part of the back naked. The elytra-bearing segments 

 are 1, 3, 4, 6, 8, — 20, 22, 25, 28, — to end. Other characters are the bidentate apex of 

 the ventral setse and the absence of dorsal setae ; but neither of these is invariable, 

 for L. microlepis from Hulule, Male Atoll, has ventral setae which have departed slightly 

 from this type, while L. arc/us*, from the south coast of England, still possesses a few 

 dorsal setae, though the notopodium is much reduced. The occurrence of one or two 

 superior notopodial setse twice as thick and strong as the others was given byMalmgren 

 in his definition of the genus t, but this character belongs only to L. elegans. The 

 head is similar to that of Lepidonotus in being directly produced into the tentacles. 



The following is a synopsis of the species here described : — 



Upper setse of ventral bundle greatly enlarged L. elegans, Grvhe. 



Upper setffi of ventral bundle more slender than rest L. maculata, sp. n. 



_ , , ■,■■,-, 1 , (Elytra cover parapodia L. niinikoensis, sn. n. 



Dorsal setffi equal in size throughout J •' . ,. , . 



[ Elytra quite rudimentary L. niicrokjAs, sp. n. 



22. Lepidasthenia elegans (Grube). (Plate 19. fig. 16; Plate 20. fig. 32.) 

 Polyno'e elegans, Grube, Actinien, Echinodermer uud Wiirmer, p. 85. 



Ileasurements, 8fc. One specimen with 98 segments was 60 mm. long and 6 mm. broad 

 (including setse) ; 36 pairs of elytra. A second specimen was 55 mm. in length and 

 had 32 pairs of elytra. 



The head (fig. 16) is small and rounded, with ill-defined eyes, the anterior situated 

 laterally. The tentacles are slender, ending in very prominent knobs and long filiform 

 tijis. The median tentacle is about four times as long as the head and one and a quarter 

 times the length of the lateral tentacles. The palps are stout and rather stumpy, ending 

 in abruptly tapering tips, and the same length as the median tentacles. 



The dorsum is provided with black pigment arranged in a chessboard pattern. Some 

 of the cirri-bearing segments are almost free of pigment, so that the pattern is inter- 

 rupted by these unpigmented bands at every fourth segment beginning at the seventh 

 till the twenty-third is reached. Then two segments which are quite pale succeed every 

 darkly pigmented one, this change being in correspondence with the alternation of two 

 cirri-bearing with each elytra-bearing segment. The general scheme of colour-pattern 



* Hodgson, T. V., Journal Marine Biological Association, vol. vi. 1900, pp. :-'o0-253. 

 t Malmgren, Anmilata Polyehaeta Spetsbergise. 



