igr?.] 



S. Kemp : Notes on Crustacea Decapoda. 



53 



As in A . indicus there is in both sexes a large hooked tooth 

 between the bases of the first pleopods. 



The petasma differs from that of any other species examined 

 in the possession of a pair of folded membranes on the anterior 

 surface. The free edge of each is furnished with a series of minute 

 hooks, by means of which the two halves of the petasma are 

 coupled. The internal lobe is truncate and slightly concave at its 

 proximal end, but is not broadly expanded as in ^. indicus. The 

 distal portion of the same lobe terminates in two large pointed 

 processes with their apices directed obliquely outwards. The 

 inner of these processes is larger and broader than the other and 

 bears on its anterior surface two large falcate spines (text-fig. 46). 



Fig. 4. — Right half of petasma, seen from in front. 



a. Acetes indicus. c. Acetes insularis. 



b. Acetes erythraeiis. d, Acetes japonicus. 



The telson resembles that of A. indicus, but the tip is not 

 quite so sharply pointed (text- figs. 5^, d). 



The ciliated and non-ciliated portions of the external border 

 of the outer uropod are separated by a small tooth. The non- 

 cihated portion in adults is from i'5 to vy times the length of the 

 ciliated part (text-fig. 7&), a proportion differring considerably from 

 that found in A . indicus. 



This species is smaller than A. indicus, large females being 

 not more than 28 mm. in length. The males from Penang are 

 only 14 mm. in length, whereas those from other localities may 

 reach 20 mm. 



The occurrence of dimorphic males in this species is a feature 

 of considerable interest, but further information is necessary 

 before the phenomenon can be profitably discussed: it is unfortu- 

 nate that such a small number of specimens are available from 

 Penang. The case does not appear to be one of seasonal sexual 

 dimorphism, for the males from Penang, all of which are of the 



