MONOGRAPH OF THE LEUCOSIAD^E. 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. Prom their small size, it is not improbable that some of them are young, but 

 certainly not of any previously described species. 



Genus Iphis, Leach, 



Char. Gen. — Testa rhomboidalis, transversa, angulis rotundatis, utrinque spina longissima horizontali 

 armata, fronte emarginato. Orbita aperta, bifissa. Antennulce fere longitudinaliter inflexae. Pedi- 

 palpi externi caule interiore sublineari, antice paulo 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 Ebalia. 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-spmosa of Adams and White is referred to the genus Arcania. 



Genus Ixa, Leach. 



Char. Gen. — Testa elliptico-rhomboidalis, processu utrinque subcylindrico a regione branchiali producto ; 

 regionibus sulco profundo separatis. Orbita supra bifissa. Pedipalpi externi caule exteriore lato, 

 obtuso, interiore lougiore. Pedes omnes filiformes, tenues. Abdomen Fcemin-iE articulo ultimo usque 

 ad oris aperturam producto. 



Species unica, Ixa cylindrtjs, Fabr. 



Cancer Cylindrus, Fabr. Mantissa, 251. Herbst, i. p. 108. t. 2. f. 29, 30, 31. 



Leucosia Cylindrus, Fabr. Suppl. 352. Latr. Hist. Nat. Crust, vi. p. 119. Licht. Berl. Mag. 1815, p. 143. 



Ixa Cylindrus, Leach, Trans. Linn. Soc. xi. p. 334. 



Ixa canaliculata, Leach, Zool. Misc. iii. p. 26. t. 129. f. 1. Edw. Reg. Anim. Cuv., Crust, t. 24. f. 1; Id. 



Hist. Nat. Crust, ii. p. 135. 

 Ixa megaspis, Adams and White, Voyage of the Samarang, Crust, p. 55. t. 12. f. 1. 

 (Senior) Ixa inermis, Leach, I. c. t. 129. f. 2. Edw. Hist. Nat. Crust, ii. p. 135. 

 Hob. 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 one species. 

 The variations which exist between any two of them are nearly as great as those which 

 have given rise to the establishment of a distinct specific name in the case of I. me- 

 gaspis of Messrs. Adams and White. I possess two specimens which were obtained by 

 Mr. Hinds, which differ so much from others, that until I had carefully examined the 

 whole of those I have alluded to, I had provisionally given them a distinct specific name. 



