I. '08. 15 



The abdominal somites are smoothly rounded above, with 

 the exception of the sixth, which is dorsally carinate. The 

 forms assumed by the sternal plates of the cephalothorax (the 

 thelycum) in the female and by the membranous expansion of 

 the endopod of the first pair of pleopods (the petasma) in the 

 male are shown in figs. 15 and 16. 



Size. — The largest Irish specimen examined is a female 

 measuring 38 mm. ; Smith has recorded an example 43 mm. 

 in length. 



Colour in life. — The carapace is red, anteriorly of a dark 

 brow^nish tint. The abdomen is also red, but considerably 

 paler than the carapace. The eyes are brown, with a golden 

 reflection ; their stalks are red, with a jet-black spot on their 

 superior and external aspect, near which is a patch of very 

 deep red pigment. Both these patches are of variable size 

 and shape. The antennal scale and all three pairs of flagella 

 are practically colourless. All the pereiopods are very dark 

 brownish red. 



There are also found, in addition to the prevailing red pig- 

 mentation, patches and suffusions of a deep blue colour. This 

 is one of the most interesting features of the species, and 

 hitherto has only been noticed very briefly. The better 

 defined patches of this pigment occupy positions much the 

 same as certain of the photophores which are known in Acan- 

 thephyra dehilis, A. Milne-Edwards.^ Now in that species a 

 deep blue pigment is invariably associated with the luminous 

 organs, in only one series of which (i.e., those at the base of 

 the pleopods) has a lens-like structure been demonstrated. The 

 question, therefore, arises whether this pigment in A. elegans, 

 although it is rather lighter in colour and much more diffuse, 

 may not nevertheless prove in some way connected with a 

 luminous function. 



In small specimens of about 18 mm. large portions of the 

 oral appendages and the basal joints of all the pereiopods are 

 suffused w^th blue pigment. In this case the pigment is in 

 solution, for it is sometimes observed flowing out from the cut 

 edge of a dissected portion. The first five abdominal somites 

 each possess inferiorly a pair of large ill-defined patches of this 

 blue pigment of a streaky character (fig. 8) and the interior 

 margins of the first and second sternal plates are also edged 

 wath the same colour. 



In large specimens only slight traces remain of these ab- 

 dominal patches and the suffusions on the oral appendages 

 and bases of the pereiopods are also much fainter ; but the 

 following, which also occur in young specimens, are found to 

 persist in the majority of the older examples : — 



On the antennular peduncle (fig. 13) : a streak on the 

 inner 'face of the penultimate joint and another, sometimes 

 merely a faint suffusion, in the middle of the basal segment 



1 Compare Bouviar's coloured figure of A. valens (1908, pi. i, fig 8) 

 with pi. Yi, fig. 1 of this paper. 



