MODIFICATIONS OF STRUCTURE IN DECAPOD CRUSTACEA. 225 



Figs. 3 a and 3 b on Plate 13 illustrate the arrangement 

 of parts in Corystes cassivelaunus, for a detailed descrip- 

 tion of which I refer to my paper on that animal (1896). The 

 only point that I need emphasise here is that the tube is 

 formed by the outer or second antennae, the first antennae 

 being situated in the interior of the tube. 



Figs. 4« and 4^* illustrate the structure of a Madras speci- 

 men of Albunea symnista, Fabr., which belongs to the 

 Hippidea. Tlie systematic position of this group of Crustacea 

 is discussed by Miers (1879). The various naturalists who 

 have previously examined specimens of this genus have all 

 failed to recognise the fact that the hairs on the antennules 

 are arranged along two longitudinal lines, and that they are 

 directed towards the axial line of the body. The figures which 

 have been published are all ludicrously conventional in this 

 respect, and represent the irregularly hairy antennae of a 

 Palinurus less incorrectly than they do the antennules of an 

 Albunea (see Milne-Edwards, ' Regne Animal,' pi. 42, 

 fig. 3; ^Crustaces,' pi. 21, fig. 9; Miers, 1879, pi. 5 ; 

 Henderson, 1893, pi. xxxviii). The converging double rows 

 of hairs interdigitate naturally to form a tube, as I have 

 recognised in A. symnista, Fabr. (PI. 14, fig. 4), Albunea 

 mi crops, Miers, and another Albunoid form (PI. 14, fig. 5) 

 which I have not been able to identify with any described 

 species, and which I here name Albunea scutelloides, 

 n. sp. 



The antennular tube expands at its base into a prostomial 

 chamber, as does the antennal tube of Corvstes. In the 

 latter case the floor of this chamber is formed by the third 

 maxillipeds (fig. 3 Z») ; but in Albunea it is formed by the 

 broadly ovate terminal lobes of the endopodites of the first 

 maxillipeds (fig. 4 b) — the homologues of the organs which in 

 Calappa form the opercular floor of the exhalant passages 

 (fig. 1 b). The prostomial chamber communicates on each side 

 by a wide aperture with the branchial chamber. The channels 

 of communication are bounded externally and ventrallv bv 

 large lamellate expansions of the basal joints of the first and 



