MONOGRAPH OF THE LEUCOSIADE. 311 
Readily distinguished from the two former species by the number and character of the 
tubercles, and from Arc. tuberculata by the spines being simple. 
Length of carapace 0:4 in. 
Of each of the last four species of Arcania, there is a single specimen in the British 
Museum. From their small size, it is not improbable that some of them are young, but 
certainly not of any previously described species. 
Genus Iputs, Leach, 
Cuar. Gen.—Testa rhomboidalis, transversa, angulis rotundatis, utrinque spina longissimä horizontali 
armata, fronte emarginato. Orbita aperta, bifissa. Antennule ferè longitudinaliter inflexe. Pedi- 
palpi externi caule interiore sublineari, anticé pauló angustiore. Pedes filiformes, graciles. 
This genus is at once distinguished from Arcania by the rhomboidal form of the cara- 
pace, in which it somewhat resembles balia. Its nearest affinity however is to Arcania, 
which it approaches in the armature of the periphery of the carapace, in the foot-jaws, the 
feet and other parts. One species of this genus only is at present known, viz. 
IPHIS SEPTEM-SPINOSA, Herbst. 
Cancer septem-spinosus, Fabr. Mantissa, i. p. 325. Herbst, i. t. 20. f. 112. 
Leucosia septem-spinosa, Fabr. Suppl. p. 351. 
Iphis septem-spinosa, Leach, Zool. Miscell. iii. p. 25. Edw. Hist. Nat, Crust. ii. p. 139. 
Iphis novem-spinosa of Adams and White is referred to the genus Arcania. 
Genus Ixa, Leach. 
`- Cuar. Gen.—Testa elliptico-rhomboidalis, processu utrinque subcylindrico à regione branchiali producto ; 
regionibus sulco profundo separatis. Orbita suprà bifissa. Pedipalpi externi caule exteriore lato, 
obtuso, interiore longiore. Pedes omnes filiformes, tenues. Abdomen F&MINÆ articulo ultimo usque 
ad oris aperturam producto. 
Species unica, IxA CYLINDRUS, Fabr. 
Ca i . Mantissa, 251. Herbst, i. p. 108. t. 2. f. 29, 30, 31. 
ri ee 352. Latr. Hist. Nat. Crust. vi. p. 119. Licht. Berl. Mag. 1815, p. 143. 
Ixa Cylindrus, Leach, Trans. Linn, Soc. xi. p. 334. 
Iva. canaliculata, Leach, Zool. Misc. iii. p. 26. t. 129. f. 1. 
Hist. Nat. Crust. ii. p. 135. 
Ira megaspis, Adams and White, Voyage of the Samarang, Crust. p. 55. t. 19. f. 1. 
(Senior) Ixa inermis, Leach, l. c. t. 129. f. 2. Edw. Hist. Nat. Crust, ii. p. 135. 
Hab. in mari Indico. Muss. Brit., Soc. Linn., Bell. ^ 
A careful examination of all the specimens of this genus to which I have access, 
amounting to about twelve, has led me to conclude that they all belong to I E 
The variations which exist between any two of them are ne x; na vm ” be d 
M siren Hbro MN MENO reges ara which were obtained by 
3 ite. I possess two : 
gaspis of Messrs. Adams and White hers, that until I had carefully examined the 
Mr. Hinds, which differ so much from ot rs, i efi ; 
whole of those I have alluded to, I had provisionally given them a distinct specific name. 
Edw. Règ. Anim. Cuv., Crust. t. 24. f. 1; Id. 
