EEPOET ON THE BEACHYUEA. 
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slender, almost filiform, with the merus and palm elongated ; fingers slightly incurved at 
the tips and denticulated on the inner margins. The ambulatory legs are moderately 
elongated and very slender, with the dactyli styliform. 
The four recent species described by authors are probably, as I have stated below, 
identical with Ixa cylindrus, Fabricius, which is probably distributed throughout the 
Indo-Pacific region from the Mauritius to the Philippines and Borneo, and also occurs in 
a fossil state in recent alluvial or perhaps quaternary deposits ( vide A. Milne Edwards, 
Ann. Soc. Entom. France, p. 156, 1865). 
Ixa cylindrus (Fabricius), var. megaspis. 
Ixa megaspis, Adams and White, Crust, in Zool. H.M S. “ Samarang, ” p. 55, pi. xii. fig. 1, 
1848. 
Manila, 1 fathom (an adult male). Presented to Dr. Willemoes-Suhm by Mr. 
Baer. 1 
Iliacantha, Stimpson. 
lliacantlia, Stimpson, Bull. Mus. Comp. Zool., vol. ii. p. 155, 1870. 
Carapace convex, ovoid or subglobose, with the lateral margins arcuated, with a pro- 
tuberance or tubercle upon the pterygostomian regions, and with three posterior lobes or 
spines, as in Myra and Persepliona. The front (in the species I have examined) is narrow 
and anteriorly slightly concave, and the orbit has more or less distinct indications of three 
marginal fissures and a wide interior hiatus. Pterygostomian channels distally very 
strongly defined and bi-emarginate. Post-abdomen (in the young male) distinctly seven- 
jointed. Eyes small. Antennules (in the species I have examined) slightly oblique. 
Antennae with a very slender basal antennal joint, which does not fill the interior 
orbital hiatus ; flagellum of moderate length. Exterior maxillipecles with the iscliium- 
1 The late Mr Bell, in his monograph of the Leucosiidse {Trans. Linn. Soc. Lond. (Zool.), vol. xxi. p. 311, 1855), 
united all the then described species of Ixa under the common designation Ixa cylindrus (Fabricius). It is probable, 
indeed, that no characters can be discovered of sufficient value to separate three of these forms specifically, but it may be 
of service here to indicate the distinctions by which the specimens in the collection of the British (Natural History) 
Museum may be at present separated. 
In that which I think to be the typical Ixa cylindrus, Fabricius ( Ixa canaliculata, Leach) the median portion of the 
carapace (circumscribed by the deep and wide lateral and postlrontal channels), has its margins sinuated or notched ; 
in the variety megaspis, Adams and White, they are entire, and in both the tubercles of the posterior margin are small 
or obsolete. A third (unnamed) variety, represented by a single female from the Philippines (Cuming) resembles 
megaspis in all particulars except that the later processes of the carapace are without the terminal spinule of that 
variety and cylindrus. 
Ixa inermis, of Leach, with which I think Ixa edwardsii of Lucas (Ann. Soc. Entom. France, vol. vi. p. 179, 
pi. iv. fig. 3, 1858) to be identical, may be distinguished by the absence of the lateral and postfrontal channels of 
the carapace (which, however, are represented in the type of inermis by an impressed suture on either side of 
the cardiac region), by the large rounded tubercles of the posterior margin of the carapace, and by the somewhat 
distally-narrowed lateral processes of the carapace (which are without terminal spinules), and may with more probability 
be regarded as specifically distinct. 
