MONOGRAPH OF THE LEUCOSIADÆ. £e 
as broad as it is long, acutely carinated on each side, tumid in the centre ; fingers flattened, 
triangular. Abdomen (male) broadly triangular. 
Colour buff and white, beautifully mottled in some specimens, in one elegantly reti- 
culated. 
- Length of carapace 0'4 in. 
Of this pretty little species there are three specimens in the British Museum, from the 
Chinese Seas. It is easily recognizable at first sight by the thin, somewhat reflexed, 
smooth margin of the carapace, and the wholly granulated surface of the arms, characters 
which I believe do not exist in any other species of the genus. The buccal opening, and 
consequently the external foot-jaws, are remarkably broad anteriorly. 
LEUCOSIA*PHYLLOCHEIRA, mihi (TAB. XXXI. fig. 5). Manibus latioribus quam longiori- 
bus, utrinque lamellatis; pedibus omnibus posterioribus articulo penultimo lato, com- 
presso, utrinque carinato. 
Hab. ad insulam Borneo. Mus. Brit. 
Carapace somewhat rhomboidal, as broad as the postfrontal portion is long ; front very 
projecting, slightly emarginate, strongly carinated at the base, with a deep hollow on each 
side; thoracic sinus terminating in a marginal notch, above and in front of the insertion 
of the first pair of legs. External foot-jaws nearly half the length of the whole body. An- 
terior legs shorter than the carapace, the arm bordered with tubercles. Wrist small and 
rounded ; hand broader than it is long, with a broad, flat, thin, laminated carina on each 
side ; fingers rather broad, flattened, the immoveable one carinated beneath. The remain- 
ing feet with the fourth joint toothed along the under side, the fifth with a single tooth 
above, the penultimate short, flattened, and having a thin carina on each side, the terminal 
one lanceolate. 
Length of carapace 074 in. 
This is certainly the most extraordinary known species of Leucosia. The form of the 
legs, and particularly of the hands, which suggested the name, at once distinguishes it 
from all others; but the most remarkable anomaly in its structure is the extent of the 
buceal opening, and the corresponding development of the external foot-jaws, the length of 
which nearly equals that of the portion of the body posterior to them. This peculiarity will 
be appreciated when it is recollected that in the normal forms the relative proportion is 
not more than one in three. Whether this structure has any relation to the habits of 
the species, we have no means of ascertaining; but it would appear probable that such a 
marked anomaly could scarcely exist in mere obedience to those abstract laws of structural 
variation, which are often as difficult of solution as they are certain in fact. 
A. single male specimen from Borneo is in the British Museum. 
Genus IzrA, Leach. 
Cuar. Gen.—Testa subglobosa, postice dentibus quatuor armata, Lun - gg T n im = 
regionem intestinalem, et una conica ad branchialem ; fronte bifido. itx suprà fissuris duabus. 
Pedipalpi externi caule exteriore recto, apice obtuso. Pedes antici longissimi, graciles, manibus con- 
tortis, antrorsüm angustatis. 29 
VOL. XXI. 
