REPORT ON THE ANOMURA. 115 



The form of the ambulatory dactyli distinguishes Polyonyx from all other genera 

 of Porcellanidse ; in other respects it appears scarcely to differ from Megalohxichium, 

 founded by Stimpson for the reception of a West Indian species, and Miers has lately 

 expressed a doubt as to the distinctness of the two genera. The ambulatory claws are 

 merely special developments of the horny spines met with on the posterior surface of 

 the dactyli in many other Porcellanids. 



Polyonyx obesulus (White), Miers. 



Porcellana obesula, White, List Crust. Brit. Miis., p. 130, 1847 (sine descr.). 



Polyonyx obesulus, Miers, Crust, in Zool. H.M.S. "Alert," p. 272, pi. xxix. fig. D, 1884. 



Habitat. — Station 186, Flinders Passage, North Australia; depth, 8 fathoms; 

 bottom, coral mud. Three specimens, one of which is a female with ova, taken from 

 the interior of a sponge {Hijjpospongia anomala, Polejaeff) ; a female with ova also 

 occurred in a free state at the same locality. 



The types in the British Museum came from the Madgica-Sima group, and those 

 described by Miers were taken on the Australian coasts. 



Section B. GALATHODEA. 



Galathcidee, Leaoli, Diet. d. Sci. Nat., t. xviii. p. 52, 1820. 

 Galatheides, Milne-Edwards, Hist. Nat. des Crust., t. ii. p. 270, 1837. 

 Galatheidea, De Haan, Crust. Japon., pp. xxii, 198, 1850. 



„ Dana, U.S. Explor. Eicped., vol. xiii.. Crust., part i. p. 401, 1852. 



„ Stimpson, Proc. Acad. Nat. Sci. Philad., p. 76, 1858. 



„ Miers, Catal. New Zealand Crust., p. 68, 1876. 



„ Haswell, Catal. Austral. Crust., p. 161, 1882. 



Carapace elongate, the regions well defined and usually rugose, with the front pro- 

 duced into a prominent and acute rostrum. Chelipedes and ambulatory limbs elongated 

 and frequently slender. Abdomen broad and well developed, simply bent, or folded on 

 itself, never closely applied to the under surface of the thorax, terminating in a powerful 

 swimming fan formed by the telson and the appendages of the sixth segment. Females 

 with four pairs of simple and slender ovigerous appendages on the second, third, fourth, 

 and fifth segments (those of the second and fourth segments may be rudimentary) ; males 

 furnished with two pairs of well-developed accessory genital organs on the first and 

 second segments (those of the first segment may be rudimentary or absent), and three 

 pairs of short, usually flattened appendages on the third, fourth, and fifth segments, all 

 of which may, however, be rudimentary. Antennules exposed ; the antennal peduncle 



