Falces a rich red brown, glabrous above, hairy beneath, inner and upper border fringed with long coarse dark hairs. Fangs very dark red brown, nearly black proximally.

Sternum yellowish brown, with a dark edge, clothed with yellowish white hairs.

Lip and maxillæ reddish brown, both with a pale border anteriorly, clothed with yellowish white hairs, inner border of maxillæ fringed with long coarse dark hairs.

Abdomen greenish grey, in some specimens yellowish grey, paler beneath, thickly clothed with yellowish white and dark hairs intermixed.

Coxal joints of legs yellowish brown. Legs otherwise same colour as abdomen but yellower, anterior pair inclining to brown, in some specimens much browner than in others.

Palpi yellowish brown.

Cephalothorax nearly one and two-thirds longer than broad, sides nearly parallel, scarcely contracted anteriorly, and cut off nearly square, sides of thorax only slightly rounded; longitudinally a very flat uniform convexity above, becoming somewhat more abrupt anteriorly, transversely only moderately convex. Normal grooves of thorax feebly indicated by darkish lines. A short deep median groove to thorax.

Mandibles equalling the cephalothorax in length, directed nearly straight forwards, cylindroid and robust, immediately beyond their origin on upper and outer side is a small prominent ovoid boss.

Upper border of groove for fang, armed with six teeth, the first small and rather remote from extremity, the second the largest of all, the other four smaller and regularly diminishing. Lower border armed with two teeth, the first close to the insertion of the fang, moderately large, the second quite small and on a level with the first of the upper border. Fang long, rather straight. Eyes of very uniform size, the posterior middle pair being the smallest; disposed in two rows, the anterior straight or curved very slightly indeed, the opening of the curve being forward. The posterior row nearly straight, but in consequence of the small size of the middle pair a line touching their posterior margins would be slightly concave backwards.

Anterior middles less than own breadth from border of face, lateral middles almost on border. Anterior middles separated from one another by own diameter, and from laterals by more than twice own diameter. Posterior middles more than own distance from anterior middles and nearly four times own diameter apart, the same distance from posterior laterals. Lateral eyes barely their own diameter apart. Anterior middles situated on a slight common eminence, they look directly forwards; anterior laterals

situated on a very slight eminence common to them with the posterior laterals, they look forward and slightly outwards. Posterior middles look upwards, posterior laterals upwards and outwards.

Sternum a long heart-shape, flat, with concave emarginations opposite the Coxæ.

Lip twice as long as broad, tongue-shaped, sides nearly parallel, but narrowing somewhat anteriorly, towards its origin it is pinched in and then widens to its insertion. Its anterior border is notched.

Maxillæ cut obliquely away from the lip and running to a sharp point anteriorly, outer border rounded, pinched in anteriorly to the insertion of the palpi, flattish, but becoming more convex towards their insertion. Abdomen ovoid. Spinnerets short, diverging, the upper and lower pair rather longer than the middle pair. Legs long, slender, clothed with yellowish white hairs intermingled with bristles at distal end of third and fourth tibial joints.

Tarsi have three claws, the two principal claws deeply combed, the posterior claw small, inconspicuous, not combed, and abruptly bent just beyond its origin.

Male palpi long, slender. The radial joint has on its outer side a bifurcate process, the lower segment thin, broad, and flattened, yellowish, with the upper border thickened, and dark brown, the upper segment thick, very much narrower than the lower segment, from which it is slightly turned away, blunt at its point, dark brown. The digital joint ovoid, prolonged, and tapering distally, and provided at its extremity with short, stout spines; the palpal organ has a coiled cirrhus about three-fourths the circumference of the organ in length. The palpi are clothed with abundant long hairs.

Female.—Colouring as male. Cephalothorax more convex above. Falces slightly shorter but more massive. Fang thicker and stronger. Epigyne pale-yellowish. A small concavity with a denticle on either side pointing inwards, posteriorly a short blunt process directed backwards.

Desis robsoni is excedingly like Desis martensii (Koch, Arachn. Austral.), which it also resembles in its marine habits. This is so interesting that I make no apology for quoting Dr. Koch's remarks in full:—

“I received from Dr. E. v. Martens, of Berlin, a third species of this interesting genus (Desis martensii). It was collected by him on coral reefs at Singapore, and kindly given to me for examination. This species is remarkable in that it has established itself in these reefs which are only temporarily uncovered by the sea; Herr v. Martens has found many specimens of the spider in this locality. * * * * * * * * * That the species discovered by Dr. E. v. Martens and Dr. Johswick, ^* can really, like our indigenous Argyroneta aquatica, Cl., live under water, is to me doubtful in the highest degree, for it is wanting in the outward visible signs of the breathing apparatus which corresponds to such submarine mode of life, and which has been anatomically demonstrated in Argyroneta aquatica ^†. It also speaks against it that yet another species of spider, an Atta, was found on the same coral reefs, and we may assume with all certainty that this is a true terrestrial form. I opine that these spiders, perhaps, in former times, were floated in an accidental manner from the land to these reefs, and now live in the holes of the coral bank, within which they withdraw at the time of flood, and which they close against the entrance of the water with a thick web. * * When once both sexes had been transferred to the coral reefs, Desis martensii would increase and form a colony there.”

I take the liberty of quoting a further valuable communication from Dr. E. v. Martens on the discovery of this interesting spider, as follows:—

“During my residence at Singapore, in October, 1861, I repeatedly visited a coral bank in the neighbourhood of New Harbour, of which large tracts were exposed above water during the ebb, at the times of new and full moon. My attention was chiefly directed to Crustacea and Mollusca; I tore off pieces of coral and broke them up to get at the creatures hidden within. To my astonishment I several times observed spiders hurriedly escaping, the idea occurred to me at first that we ourselves had brought them from the shore in our clothing. I generally went with the late staff-surgeon, Dr. Johswick, in a little skiff pulled by a Chinese from the frigate ‘Thetis’ which lay in the roadstead, or from the town, distant about half-a-league from the coral reef. This suspicion was rendered unlikely by the frequent repetition of the event, and conclusively disproved, as Dr. Johswick found a web of undoubtedly one of these spiders in an old dead mussel shell, between the coral, stretched sheet-like in the cavity of the shell.” ^‡