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CRUSTACEA OF THE MERGUI ARCHIPELAGO. 157 
abnormal individual. In the male the chelipedes gradually appear 
more elongate, according to the greater age of the individuals : 
é. g., ina small specimen, the cephalothorax of which is only 
20 millim. broad, the chelipedes, being 80 millim. long, are one 
and a half times as long as the breadth of the carapace; the 
chelipedes of this specimen only project for a short distance 
beyond the lateral margins of the cephalothorax, the arms 
scarcely reaching to the distal end of the first third of the 
meropodites of the third pair of legs. In the largest specimen, 
on the contrary, the chelipedes are nearly two and a half times 
as long as the breadth of the cephalothorax, and they are very 
elongate, the arms reaching nearly to the distal end of the mero- 
podites of the third pair of legs. The arms are triquetrous in the 
male, presenting an upper, an anterior, and a posterior surface ; 
they are somewhat thickened near the proximal extremity, and 
also, although not so much, at the distal end. The ‘‘musical crest”’ 
is situated near to the proximal extremity of the anterior margin 
of the upper surface of the arm, and on the margin itself, so that 
it lies exactly opposite to the infraorbital ridge, against which 
it is moved and rubbed by the animal. In the female there is 
no trace of the musical crest. 
As already stated, the chelipedes are comparatively much 
shorter in young male specimens than in the adult. In a 
young individual, the cephalothorax of which is 20 millim. 
broad, the musical crest is placed on the middle of the anterior 
margin of the arm; so that at a still younger age it is probable 
that the crest is situated near the distal extremity of the arm (as 
in Helice), and that it gradually proceeds towards the proximal 
extremity, in consequence of the growth of that part of the arm 
lying between the crest and the distal extremity, the proximal 
part not increasing in length. In the same specimen the hands 
are less elongate than in the adult, and the fingers are a little 
longer than the palm, whereas the immobile finger is scarcely 
curved downward. 
The female specimen, carrying eggs, is scarcely more than 
20 millim. broad. Its chelipedes are equal, project but little 
beyond the lateral margins of the carapace, and are even smaller 
than those of the male specimen of equal size. The fingers 
are nearly once and a half as long as the palm. 
