"Among the various genera closely allied to Kepon, Duvernoy, 1840, Leidya, established by Cornalia and Panceri in 1861, is the only one founded on the male sex, and this is unique in the possession of elongate uropods. Among those dependent on characters of the female, Gigantione, Kossmann, 1881, alone has in that sex biramous uropods. Ergyne, Risso, 1816, the Portunicepon of Giard and Bonnier, agrees with Kepon and is distinguished from the rest by having the branches of the pleopods more nearly equal. Caiicricepon, Giard and Bonnier, 1887, has a medio-dorsal boss on each of the last four peraeon-segments. Trapezicepon, Bonnier, 1900, has none of these. Grapsicepon, Giard and Bonnier, 1887, has a medio- dorsal boss on each of the last two peraeon-segments, and herein it agrees with the new genus, which differs from it in that, instead of a simple boss on the sixth peraeon-segment, the boss there is strongly trifid. The head also furnishes a striking character for the new genus, being formed as it were of two short stout cylinders with rounded ends, of which the inner ones look as if they were flattened below where they meet, forming nearly a right angle." (Stebbing, 1904)
"The appearance of the prominent white head has been already described. The peraeon from its opaque orange colour did not show clearly either the division of the segments or the contour of the lateral bosses, but the triple boss in the middle of the sixth segment was white and stood out clearly. The single median boss on the seventh segment was also white and directed somewhat upwards. When mounted this proved to have its rounded end marked off by a slight constriction. The laminae of the first pleon-segment are very large, strongly tuberculate on the upper surface and edges. The following pairs are successively smaller.
The first antennae are very small, three-jointed; the second a little larger, five-jointed.
The ' buccal rostrum ' and the pair of maxillipeds, each member of which is consolidated into a single piece of great breadth at the centre with a narrow incurving apex to represent the terminal joints, differ very slightly from the corresponding parts in Cancricepon (see Bonnier, op. cit. PI. VII. figs. 3, 4). The strong muscles are conspicuous in their large but shallow cavity. Below the maxillipeds is that which Bonnier designates as the lower cephalic lamina. This in Cancricepon elegans, Giard and Bonnier, forms three lobes on either side in such a way that the outermost are produced furthest backward and the innermost the least far. In the present species the central piece, though pretty strongly emarginate, is scarcely bilobed, and by extending back much beyond the two lateral pairs of lobes appears to differ from the corresponding part in all the neighbouring genera.
The vast marsupial plates attached to the minute first gnathopods have as usual the anterior section underlying much of the maxillipeds, this part being produced on the inner (upper) surface into a broad sculptured lappet overlying a piece of the plate's hinder section.
On the outer (ventral) surface the two sections pass smoothly into union, the upper one having a convex groove near the proximal part of the leg. The first gnathopods differ from the rest of the limbs chiefly in having the fifth joint smaller and more completely over-lapped by the compact sixth joint. The second and third joints increase in size in the successive pairs of limbs to the fourth peraeopods. In both the fourth and fifth peraeopods the second joint is rather remarkable for the bulging of the two margins, and the third joint is greatly widened distally.
The pleopods have the outer branch similar to the pleural laminae of the segment, but smaller, and the inner branch very much smaller than the outer, with the margins a little irregular, at least in the earlier pairs, and perhaps in all.
The uropods are single-branched, long and slender, very much crumpled in the spirit specimen.
Length 3 mm., with a breadth of about 2'5 mm.
The specific name is chosen in compliment to M. Jules Bonnier, whose finely executed and instructive work on this group of the Isopoda has been more than once referred to above. In the same bottle with the specimen just described there were four other isopods, which I am disposed to regard as belonging to the same species, although, as Sars rightly argues. Idem propterea non est, quia captus ibidem.
The present specimen is probably not mature, since it has second antennae reminiscent of the cryptoniscus-stage. The pleopods also are more strongly developed than in the adult of Cancricepon elegans, but in correspondence with the bopyrian stage of that species. No dorsal or ventral bosses were perceptible.
The eyes are dark, longer than wide. The limbs all nearly alike, with the fourth and fifth joints very small, the sixth compact. The terminal segment of the pleon is bilobed, the lobes a little prolonged, each with a minute seta at the apex and another at the side.
Length estimated at half a millimetre.
The cryptoniscus-stage, whether of this or some other species, was represented by three specimens, smooth, narrow, sharply tapering to the uropods, the head broader than long, with a pair of gleaming eyes. In describing Liriopsis pygmaea (Rathke) Sars says, ' eyes very distinct, each consisting of a dark pigment, within which is imbedded a single rather large, refractive lenticular body.' The dorsal view which he gives of that species is in fair agreement with the specimens now under notice, but in these the ocular pigment is not dark, and the fourth and fifth peraeopods have not the peculiar shape characteristic of Liriopsis.
The first and second gnathopods are compact, subchelate, with the fifth joint apparently in coalescence with the sixth. The peraeopods are slender, all having the fourth and fifth joints very small, the fifth triangular, underriding the sixth. The second joint is widest at the middle and narrow at both ends; the third, which is rather shorter but broader, is narrow only at the base ; the sixth like the second and third has a convex outer and more or less straight inner margin ; near the apex of the latter it carries a fine spine and in the first three pairs two minute spinules on the widened apical margin, but a single spine on the comparatively narrow apex of the last two pairs. The finger is thin, slightly curved, longer on the fourth and fifth peraeopods than on the three preceding pairs, but in none longer than the sixth joint.
The pleopods have a broad but short peduncle armed at the inner angle with two long spines. The rami are short, not longer than the peduncle, each carrying four long plumose setae, the outer which is the less robust having in addition a short plumose seta at the outer angle.
The uropods have short peduncles, quite as broad as they are long. The outer ramus, scarcely longer than the peduncle, carries a long seta and two that are shorter. The inner ramus, more than twice the length of the outer, tapers to the apex, which nearly agrees with that of the outer ramus in armature.
Length 1"5 mm., with a breadth of about 0'4 mm." (Stebbing, 1904)
"The specimen had been already extracted from the host, Tylocaricinus styx, which was taken at ' Hulule, Male Atoll, Maldives,' and which showed on the left branchial region of the carapace the cavity that had been occupied by the parasite." (Stebbing, 1904)
"This minute creature bears a very near resemblance to the males of Cancricepon elegans and Grapsicepon edwardsi, as figured by M. Bonnier. It would be an extraordinary chance that the female parasite of Tylocarcinus should have reached England from the Maldives, without a male of its own species, but accompanied by a male belonging to some other species of the same family." (Stebbing, 1904)
