MONOGRAPH OF THE LEUCOSIAD^. 291 



as broad as it is long, acutely cariuated on cacli side, tumid in the centre ; fibagers flattened, 

 triangular. Abdomen (male) broadly triangular. 



Colour buff and wliite, 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 Museimi, from the 

 Chinese Seas. It is easily recognizable at first sight by the thin, somewhat reflexed, 

 smooth margin of the carapace, and the wholly granidated sm-face 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 phtllocheira, mihi (Tab. XXXI. fig. 5). Manibus latioribus quam longiori- 

 bus, utrinque lamollatis ; pedibus omnibus posterioribus articulo peniiltimo 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 hoUow on each 

 side ; thoracic sinus termiuating 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 immovealile one carinated beneath. The remain- 

 ing feet with the foui-th joint toothed along the under side, the fifth with a single tooth 

 above, the penultimate short, flattened, and ha\'ing a thin carina on each side, the terminal 

 one lanceolate. 



Length of carapace 0'4 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 aU others ; but the most remarkable anomaly in its structure is the extent of the 

 buccal 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 recoDected that in the normal forms the relative proportion is 

 not more than one in three. Whether this structm-e 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 difiicult of solution as they are certain in fact. 



A single male specimen from Borneo is in the British Museum. 



Genus Ilia, Leach. 



Char. Gen. — Testa subglobosa, postice dentibus quatuor armata, quarum utrinque una compressa ad 

 regionem intestinalem, et una conica ad branchialem ; fronte bifido. Orbita supra fissuris duabus. 

 Pedipuljn externi caule exteriore recto, apice obtuso. Pedes antici longissimi, graciles, manibus con- 

 tortis, antrorsum angustatis. 

 VOL. XXI. 2 Q 



