MACRUROUS DECAPODA OF THE SUDANESE RED SEA. 369 



specimens. The form of. the first pair of legs in these specimens, as far as 

 they are present, may be noted as follows : — 



(1) Two specimens have both the first pair of legs missing. 



(2) One specimen, 8 mm., lacks the left leg of the first pair. The 

 right one is a regenerated limb, very like the smaller chela of the 

 female as figured by Ooutiere (fig. 129/), but with the carpus 

 relatively much shorter. 



(3) One specimen, 5 mm., lacks the right leg of the first pair. The 

 left one is exactly of the same form as the smaller chela of the 

 female, and is in this specimen not a regenerated limb. 



(■A) One specimen, 9 mm., has both legs of the first pair present and 

 they agree in all particulars with Coutiere's descriptions and figures 

 (fig. 129 e and d). 



(5) One specimen, 9 mm., lacks the left leg of the first pair. The right 

 one is of the same form, size, and proportions as shown by Ooutiere 

 for the larger chela of the male (fig. 129 c), but the immovable 

 finger bears a broad high tubercle in the centre of its inner margin, 

 and the movable finger has a prominent smaller tubercle on its 

 inner margin proximal to the tubercle on the fixed finger (PI. 28. 

 fig. 25). 



Kemp (1915, pp. 289-299) has recently described and discussed at length 

 a most remarkable and interesting case of " trimorphism " among the males 

 of a new species of Alliances, A. polymorphus, Kemp, discovered by him in 

 the Ohilka Lake, India. He found three forms of males as follows : — 



Form I. Small in size. First pair of legs asymmetric, one enlarged, 

 without tooth on fixed finger, the other slender and of the 

 size and proportions of those of the female. 

 Formll. Large in size. First pair of legs symmetrical, no tooth on 



fixed finger. 

 Form III. Of same size as Form II. First pair of legs asymmetric. 

 One of them with a prominent rounded tooth on the fixed 

 finger, the other without such tooth. 



In all three forms the appendix masculina on the second pleopods was well 

 developed, but form I. was met with in the non-breeding season only, and 

 forms II. and III. in the breeding-season only. 



After discussing the phenomenon in all its aspects, Kemp inclines to the 

 opinion that forms II. and III. are true dimorphic forms developed simul- 

 taneously at the breeding-season from the non-breeding form I. 



Regarded in the light of Kemp's observations the males of A. djiboutensis 



