340 The Philippine Journal of Science im 



chelipeds of the male Palaemon carcinus are sexual adorn- 

 ments. In our local form of Palaemon carcinus the chelipeds 

 of young males, young females, and mature females are blue 

 or lavender, while the chelipeds of the old males are very dark, 

 inconspicuous blue. I can readily believe that the blue color 

 is an adornment, but I can hardly believe that it is attractive 

 to the females, even if we assume that they have color sense, 

 as these palaemons live in water which is far from clear. A 

 study of the habits of the palaemons may throw some light 

 on the meaning of these large chelipeds. 



Localities. — We have in our collection 41 males and 21 females 

 which were collected from Pasig River, San Juan River (a 

 tributary of Pasig River), and Laguna de Bay, the source of 

 Pasig River. All of these bodies of water are in the neighbor- 

 hood of Manila, Luzon. Since the above was written, several 

 large specimens have been added to the collection by A. L. Day, 

 who collected them in Naujan Lake near Calapan, Mindoro. 



Palaemon philippinensis sp. nov. Plate II, figs. 2 and 2a-m. 



This species presents much variation in the shape and general 

 appearance of the rostrum. The proportion of the carpus to the 

 merus of the chelipeds is not constant, the carpus increasing 

 in length faster than the merus as the animal grows longer. 

 Another characteristic of this species (possibly of all species of 

 Palaemon) is the occurrence of dimorphic males; that is, some 

 of the males of medium size have chelipeds of about the 

 same length and shape ("males feminises" of Coutiere) 22 as 

 those of the females of the same size, and other males of small 

 or medium size, but usually covered with brownish sediment, 

 have the characteristics of the largest and undoubtedly mature 

 males; namely, enormously long chelipeds with well-armed and 

 gaping fingers (young mature males). In our collection the 

 "males feminises" far outnumber the other males (Table II). 



"Ann. Sci. Nat., Zool. (1900), 11, 269. In the present paper the follow- 

 ing terms are used to distinguish between different forms of males : "Young 

 males," "males feminises," "young mature males," and "old mature males." 

 The distinction between the different forms is not always clearly denned, 

 but the terms are used for convenience in description and for the purpose 

 of indicating my attitude in reference to Coutiere's statement that di- 

 morphic males exist among palaemons. It should be understood, however, 

 that I have no proof that the "males feminises" are nonbreeding in- 

 dividuals or that the "young mature males" are breeding individuals. The 

 former term is used for medium-sized male specimens that have chelipeds 

 like those of the females and the latter term is employed for such small 

 or medium-sized males as have chelipeds like those of the largest males. 



