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Show 296 MR. CYRIL CROSSLAXD OX THE [Feb. 16, broad, two are rather less elongated, and one is somewhat less broad. The acicular setae project more or less and so are subject to wear in use, as a result of which the hooks and guard are not often found perfect (when they correspond exactly with Gravier's figure) but usually more or less damaged. The larger and posterior hook being the most exposed is seen to wear away the faster, so that in many cases where attrition has gone furthest, the remnants of both hooks are of nearly the same size, the whole then resembling Gravier's figure of this seta in E. mutabilis. A consideration of the range of variability set forth above enables us to estimate the grounds for regarding Gravier's two species, mutabilis and perrieri, as synonymous with afra Peters (collar is Grube). The former (I. c. p. 245) differs from the examples regarded as typical in its uniform pigmentation, the position of the eyes, and the complexity of the gills. The eyes are placed on the swollen bases of the median pair of tentacles, a condition found frequently in these specimens of E. afra (PI. X X . fig. 5). (From Gravier's text and an examination of the present examples, it is evident that this appearance is exaggerated in the fig. I. c. pi. xiii. fig. 71.) The gills are unusually complex for a specimen of this size, but agree in size and distribution with the above. The setae figured for E. mutabilis differ slightly from those given for E. collaris (cf figs, on pp. 247 & 253 I. c), but, as explained above, such variations are common in this as in other species of the Eunicidae. The jaw-apparatus calls for no remark, its formula being 4 - 4 : 4 + 3 - 5. In his description of the buccal segment of both E. mutabilis and E. perrieri, but not in that of E. collaris (= afra), Gravier mentions a projecting lobe laterally, which is present also in all the specimens here dealt with and seems rather characteristic of the species. For its appearance and proportions see the side view of the head figured, PI. X X . fig. 2. As regards the supposed new species E. perrieri, the arrangement of the pigment in a mosaic so frequently met with is sometimes artificial and due to the wrinkling of the skin, and a similar coloration of the tentacles (the distal part being uniformly pigmented, not banded) is common, though not the rule. The groove behind the middle tentacle, described here but not mentioned in the cases of E. mutabilis or E. collaris, and figured by Gravier on pi. xii. fig. 58, is more or less distinct in all the present specimens. Often its sides are raised into distinct lips, which form the white streak described above in the case of the Prison Island specimen (see PI. X X . fig. 5). The more ventral position of the first few feet has already been remarked upon. The gills in large specimens with their twenty filaments are much more complex than any hitherto met with in East Africa or the Maldives. The differences between the descriptions and figures (I. c. p. 234) of setae given for E. collaris and E. perrieri are very trifling, even more so than in the case of E. mutabilis. |
