250 CEYLON PEARL OYSTER REPORT. 



is, however, probably due to a temporary protrusion of the setae, but it may serve to 

 account for the alleged difference between L. trissochatus, Gr., and L. indicus, 

 Kinberg. The hastate setae can clearly be retracted and protruded at will. In one 

 segment they are projecting on one side, retracted on the other. The elytra are 

 sparsely covered with smooth obtuse pustules of varying sizes, the smaller and more 

 numerous occupying a submarginal position. The margin of the elytron is quite 

 smooth. 



As indicated by Grube in 1869, this species presents a cryptocephalous condition, 

 as in the later described species L. cryptocephalus, the head being concealed below a 

 projecting collar formed by the second segment. The dorsal cirri are smooth, with a 

 terminal flagellum and a subterminal swelling. The palps are beset with conical 

 papillae, and terminate in a smooth attenuate extremity (seen in one of the palps 

 only). The ventral setae have simple hamulate extremities (not bidentate) with the 

 usual subterminal fringes. 



Halosydna zeylanica, n. sp. Plate I., figs. 12 and 13. 



Total length about 15 millims., width 2 millims. to 2 -5 millims. Commensal on 

 Astropecten, Ceylon seas. 



Body much flattened, extremely fragile, elytra smooth, colourless, covering the 

 dorsum, leaving parapodia exposed, lightly attached to the elytrophores. The 

 prostomium is divided by a shallow linear groove into two halves, upon which no 

 eyes were observed, and the bases of antennae and tentaculum are somewhat concealed 

 below the frontal border of the head, though arising at one level, as seen in frontal 

 view. The number of segments may be as many as 50, but this will depend upon age 

 and variation, and the same applies to the number of the elytra, the highest number 

 observed being 24 pairs. 



The chief character is presented by the distribution of the elytra on the following 

 segments : II, IV., V., VII., IX., XI, XIII, XV, XVII, XIX, XXI, XXIII, 

 XXVI, XXIX., XXXII, XXXIII, XXXV, XXXVII, XXXIX., XII, XIIII, 

 XIV., XLVII, XIIX. The peculiarity here is the occurrence of successive elytra on 

 segments XXXII and XXXIII. a point which I have verified on three specimens. 

 In the specimen of which the elytral formula is given above, the elytra were lost 

 from a number of the posterior segments but present on No. XIIX. 



The dorsal ramus of the parapodium is very small, and the setae which issue from it 

 are few in number, plain and hyaline. Foreign particles adhere to all the setae 

 individually throughout their exposed portions. The ventral setae have the form 

 shown in Plate I, fig. 13, a plain apex slightly curved, and at some distance removed 

 from it a dilatation with a projecting semilunar cusp. The number of ventral setae 

 varies, but is about 12. 



The ventral cirri are shorter than the ventral ramus, arising from a prominent base. 

 The dorsal cirri are plain structures occurring on the segmenta nuda. arising from a 



