258 CEYLON PEARL OYSTER REPORT. 



appears in the stout setae from the centre of the ventral fascicle. In Plate II., 

 figs. 43 and 44, two of these setae, one from the right sixteenth foot of each species, 

 are shown side hy side. In Ps. zeylanica the declivity of the articular surface of the 

 shaft is greater, and below the apex of the shaft there is a very distinct semilunar 

 cusp which is not present in the seta of the same order in Ps. rigida. The other setae 

 show close correspondence, and here, as there, some of them are distinctly bidentate, 

 but the difference noted appears to be constant. 



Sthenelais zeylanica, n. sp. Plate II., fig. 48. 



A fragment with extruded proboscis, 15 millims. long, 5 millims. wide, in company 

 with Hyalinoecia camiguina, was dredged off Foul Point, Trincomalee, Station XXV., 

 8 fathoms. 



This species is closely allied to Sthenelais boa, but differs in several well-marked 

 points. The prostomium carries four eyes in front, two on either side of the stout 

 ceratophore with its aliform lobes (characteristic of the genus) ; the tentaculum impar 

 borne upon the ceratophore is not very long, about as long as the ceratophore and the 

 prostomium together ; the palps are long, nearly as long as the extruded proboscis. 

 The free margin of the latter carries both dorsally and ventrally a row of eleven 

 evenly disposed papillae. 



The scales are carried on the usual segments II., IV., V., VII., IX 





* * # * XXVII. , XXVIII. , XXIX., &c, becoming consecutive at segment 

 XXVII. In the condition of extruded proboscis the dorsum of the third segment 

 hardly shows, and the first two scales appear to occur on consecutive segments until 

 they are pressed apart. The general character of the scales (their pronounced reniform 

 shape, the tuberculation of the surface and the fimbriation of the margin) resembles 

 that described and figured by Professor McIntosh for Sthenelais boa (' Ray Soc. 

 Mon.,' 1900) ; the fimbriae of the outer margin are acuminate, others which occur on 

 the posterior margin are blunt ; the tubercles are thickly scattered over the whole 

 surface except near the anterior border of the inner lobe and near the corresponding 

 border of the outer lobe ; brownish pigment occurs all over the exposed portion of 

 the scale. 



The characters upon which I rely for specific differentiation are presented by the 

 parapodia of the body-segments. In Sthenelais boa there are four principal groups of 

 setae, the dorsal plumose capillary setae, the superior ventral plumose spiniform setae, 

 the mid-ventral compound bidentate falcigerous setae, and the inferior ventral com- 

 pound setae with articulate bidentate appendix (cf. McIntosh, op. cit., 1900). In 

 Sth. zeylanica instead of the group of superior ventral spiniform setae we have, 

 composing this group, a few of the same kind of slender compound setae with 

 articulate appendix as occur in the inferior ventral group, and the spiniform setae are 

 not represented in the ventral ramus of the parapodium. The setae themselves are 

 not sensibly different from those of the corresponding forms in Sth. boa (Plate II., 



