Description.

Mode of Occurrence and External Characters.—Mr, Hedley has supplied me with the following field notes: "The centre of the principal islet of Funafuti Atoll is occupied by a large bare flat, surrounded by a hedge of Rhizophora—this locality is described (ante p. 10) as the Mangrove Swamp. At the north end of this, near the holes through which the tide ebbs and flows, are numerous, shallow, sandy or muddy puddles covered at half tide; the most prolific being some under the shade of the mangroves. In such a puddle, 3 inches deep and 2 feet across, a dozen specimens might be found. The animals were best secured by taking up a handful of wet mud and combing the fingers carefully through it. The primrose yellow of the Ptychodera distinguished the least exposure of its body, and it was carefully washed off the fingers into a vessel of water. Even with care many specimens were torn. The two species were found associated together."

The external characters alone suffice to mark off this species from all the described species of the genus Ptychodera.

P. flava, as Willey has shown, is at once characterised by the great development and extreme ventral origin of the genital wings (or better, genital pleura, as Willey has suggested), and thus belongs to Spengel's provisional subgenus Chlamydothorax, of the family Ptychoderidæ. P. hedleyi, on the contrary, is entirely devoid of genital pleura, and is hence to be associated with P. minuta and P. sarniensis, in the subgenus Ptychodera (sensu stricto). The complete specimens of this species at my disposal vary in length from about 6 to 14 cm.

Mr. Hedley supplies the following notes on the mode of preservation: "On arriving at the camp, the tube containing the take of Ptychodera was emptied into a photographic dish filled with sea water; a little cocaine was added, which seemed to induce the animals to crawl about freely. After four or five hours they had rid themselves of mud and mucus, and were killed by a weak solution of chromic acid. Having remained in this for twelve hours, they were finally transferred to three per cent. solution of formol."

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Proboscis.—The proboscis of this species, like that of the P. minuta and P. sarniensis, is relatively short. It has a greatest length of 9 mm., and a breadth of 5 mm., i.e., its length is not quite double its breadth. In form it is somewhat egg-shaped, or more accurately, its outline may be compared with that of the human tongue. A distinct median sulcus is present, on its dorsal surface, in some specimens, but not in all, and may simply be due to contraction in preservation.

Collar.—The collar appears about as broad as long, with a greatest length and breadth each of 5 mm. It is considerably shorter than the proboscis, in the proportions of 5·9 and 4·7 in two individuals.

The five regions of the collar are distinct, and in their relations are characteristic for the species. The first region includes the anterior free part of the collar, and occupies about a third of its entire extent. Its free margin is slightly crinkled, but is not markedly expanded frill-like, as in P. australiensis.^* This free part of the collar narrows posteriorly, and passes over into the second region, occupying the middle third of the collar.

This second region appears of a darker colour than the first, and is somewhat broader than the latter. It forms a distinct circular cushion, narrowing anteriorly where it joins the first, and broader posteriorly where it adjoins the third region. The posterior third of the collar, constituting its broadest portion, includes the third, fourth, and fifth regions.

The third and fifth regions are formed by two prominent circular ridges of about equal size, and are separated from each other by a circular groove constituting the fourth region. The circular rim of the fifth region forms the posterior margin of the collar, and has a distinctly greater transverse diameter than the succeeding branchio-genital section of the trunk, so that the collar appears distinctly marked off from the latter.

In the specimens the collar shows distinct longitudinal grooves, no doubt produced by the contraction of the collar musculature.