I9I5-] 



Fauna of the Chilka Lake : Crustacea Decapoda. 



291 



the first legs have attained. In the smallest males (five specimens) one of the first 

 legs, either right or left, is identical in structure with that of the female, while the 

 other is greatly enlarged, the fingers of the chela being curved and not provided 

 with teeth (text-fig. 316). In other males (two specimens) both legs of the first pair 

 are equally enlarged, each being closely similar to the large limb borne by the preced- 

 ing form (text-fig. 31c). In others again (two specimens) both legs are enlarged, 

 but asymmetrical ; one limb, except for the greater number of spines on the merus, 

 is similar to that in the preceding group, while the other is a little larger and, apart 

 from more trifling differences in forms, is provided with a huge rounded tooth on 

 the fixed finger (text-fig. 3id). 



The characters of the nine males may be tabulated thus : — ■ 



Date of 

 capture. 



Length of 

 carapace. 1 



First peraeopods. 



1914. 



Sept. 9th 

 Sept. 10th 

 Sept. 12th 



mm. 



2-6 



25 

 3'2 

 28 



23 



Form I, text-fig. 31&. 



Asymmetrical. One, either light or left, enlarged, without tooth 

 on fixed finger and with few spines on merus. Other slender, 

 of proportions similar to those of female. 



March 22nd 



50 

 4'3 



Form II, text-fig. 31c. 



Symmetrical. Both enlarged, without tooth on fixed finger and 

 with few spines on merus. 



March 16th 



4'4 

 4-1 



Form III, text- fig. 31^. 



Asymmetrical. Both enlarged, with numerous spines on merus. 

 Right leg in both specimens with large rounded tooth on fixed 

 finger. Left, in one specimen without tooth on finger (i.e. 

 similar except for spines on merus to Form II), in the other 

 specimen missing. 



In all these specimens the appendix masculina on the second pleopods is well 

 developed ; there is thus no doubt regarding their sex. Also, it is in my opinion im- 

 possible that the small limb found in Form I is the result of regeneration. In almost 

 all cases it is easy to distinguish a limb that has been broken off and subsequently 

 grown again and it is, I think, inconceivable that in each of the five individuals of 

 this form it should be equally and perfectly re-developed. 



The case therefore is one of trimorphism, at any rate in a somewhat loose appli- 

 cation of that term ; but the specimens are so few in number that I have found it 



1 The measurement is taken from the posterior mid-dorsal edge of the carapace to the tip of the 

 eye. 



