OCR Text |
Show 1900.] POLYNOID FROM NEW' ZEALAND. 979 close together that at first sight a single pair only appears to exist, but its anterior limit is not distinctly marked, as it is produced into the cylindrical bases of the three tentacles \ The length up to the base of the median tentacle is about equal to the breadth (2\ m m . by 2\ m m . ) . The median tentacle is slightly longer than the lateral, and its base is depressed very slightly belowr those of the lateral pair, which thus form a shallow V-shaped groove behind it. The median tentacle is about 6 m m . long; the lateral pair being 5 m m . each, measured to the posterior end of the base. Arising between the prostomium and peristomium, on the lower surface of the head, is a pair of palps about 9 m m . long, which just below the tip narrow suddenly to a fine point; they bear 7 to 9 longitudinal rows of papillae, which take a somewhat spiral course. The peristomium bears a pair of considerably modified parapodia. Each consists of a conical base bearing two cirri, a dorsal and a ventral, which resemble the tentacles (Plate L X I . fig. 4). On the anterior dorsal surface of the base a very small bunch of hairlike bristles protrudes, corresponding to the notopodial hairs of succeeding segments. O n the ventral surface of the head the mouth has been already sufficiently described; only one point remains to be noticed, namely, that the ventral cirri of the second segment are elongated and bulbous below the tip, just like the preceding pair. They are generally inclined towards the mouth, and are termed the buccal cirri. In some specimens the ventral cirri of the next segment showed a tendency to swell below the tip, more marked than in those further back (Plate L X . fig. 2). Elytra.-A reference to fig. 1 will give a better idea of the arrangement of the elytra than any description. They are attached to the body by a considerable area, the " areola," of an oblong form and of considerable breadth. The corresponding area on the body is the elytrophore (Plate L X . fig. 3), and lies obliquely transverse on the flattened parapodial ridge mentioned above. The colour of a typical elytron is a warm, brown behind a line taken transversely across about its middle, the colour advancing forwards somewhat at the inner end (indicated by dots in Plate LXII. fig. 10). The part covered by the preceding elytron is light buff, and this colour extends backwards over the anterior slope of the areolar ridge. The elytra vary considerably in size and shape according to their position, the terminal ones being smaller. Plate LXII. 1 In Lepidonotus it is usually stated that the " prostomium is produced into the base of the lateral tentacles " ; as a matter of description this is true, but, from the comparative anatomy of the group, it appears that the cylindrical "prolongation" (marked b.t. in the figure) should be regarded as the base of the tentacle fused with the anterior margin of the prostomium : this margin is in the present annelid just indicated by a faintly marked, oblique line ; and it this be compared with the prostomium of Harmothoe and others, this interpretation seems reasonable.-W. B. B. PROC ZOOL. Soc-1900, Xo. LXIV. 64 |