CRTJSTACEA OF THE MERGUI ARCHIPELA&O. 163 



one, wiiich is united with the chief portion at its base, so that 

 each lobule is transversely sulcate near its posterior end. A 

 similar structure is also found in M. distinctus, but in this 

 species the lobules of the orbital portion, 12 or 13 in number, 

 are much smaller, and decrease more gradually in size. The 

 lobules of the postorbital portion decrease more regularly in 

 size, and are rather granuliform. In the female the infraorbital 

 ridge is not prolonged behind the orbits, so that a postorbital 

 portion is wanting; the ridge is composed of 18-20 minute 

 truncate teeth, the first ten or twelve of which are nearly equal, 

 and the posterior ones only decrease slightly in size. 



This species, in the pterygostomian regions of its cephalo- 

 thorax, and in the form and size of the male abdomen and of 

 the outer foot-jaws, agrees with M. distinctus. The anterior 

 margin of the buccal cavity also presents the same structure 

 and form in both species. 



The chelipedes of the male differ from those of M. distinctus. 

 In the adult specimen the left chelipede is much larger than the 

 right, but in the younger specimens (the cephalothorax of which 

 is less than 20 millim. broad) they are equal to one another. 

 The arms do not project so far beyond the lateral margins of the 

 cephalothorax as in M. distinctus ; when comparing specimens of 

 both species with one another (the cephalothorax of which is 

 17 millim. broad), the arms scarcely project beyond the lateral 

 margins of the carapace in J/", dentipes, whereas in M. distinctus 

 they reach a little beyond even the middle of the meropodites of 

 the third and fourth legs. In the adult specimen, however, the 

 arms project nearly as far laterally as do those of the smaller 

 W. distinctus. The arms have nearly the same form and struc- 

 ture in both species, the upper surface being slightly enlarged 

 towards the distal extremity ; the " musical crest " lies on the 

 middle third of the anterior margin, which is minutely denticu- 

 lated at its distal half, like the posterior margin. In younger 

 individuals the musical crest is found near the distal extremity, 

 as in Selice tridens, de Haan. 



The wrist is somewhat granular above, especially on its pos- 

 terior and anterior margins. The larger hand of the adult male 

 is about twice and a half as long as it is broad at the base 

 of the fingers. Though closely resembling M. distinctus, the 

 palm is, however, a little less elongate, its length being in pro- 

 portion to its breadth (height) at the base of the fingers as 



11* 



