ix, d, 4 Cowles: Palaemons of the Philippine Islands 329 



male individuals (short chelipeds), varying in body length from 

 100 to 240 millimeters, show that the rostrum overreaches the 

 antennal scale. In specimens from 100 to 110 millimeters long 

 the rostrum extends almost one-third of its length beyond the 

 antennal scale, and this distance gradually decreases until in 

 individuals 240 millimeters long it overreaches the antennal 

 scale only slightly. Finally, in 4 large males (chelipeds enor- 

 mously developed) measuring from 250 to 320 millimeters, the 

 rostrum fails to reach the tip of the scale. In fact, in another 

 male only 240 millimeters long but with the chelipeds enormously 

 developed the condition is similar. While this gradual decrease 

 in the length of the rostrum might be explained by the as- 

 sumption that during the life of these palaemons the tip is 

 repeatedly broken off and then partially regenerated, it is hard 

 to believe that such is the case, considering the uniform character 

 of the decrease shown by the series at hand. 



The descriptions or figures of Palaemon carcinus by Fabricius, 7 

 Herbst, 8 M. Milne-Edwards, 9 Ortmann, 10 de Man, 11 and Hender- 

 son and Matthai 12 all indicate that the rostrum extends beyond 

 the antennal scale, while Henderson's 13 description and 

 Rumphius's 14 figure show that these authors have examined some 

 specimens in which the rostrum extends to the tip of the antennal 

 scale only or fails to reach it. Von Martens 15 mentions the 

 fact that the rostrum of Palaemon carcinus from Luzon is 

 strikingly short. Henderson finds great variation in the length 

 of the rostrum of P. carcinus from India, some specimens show- 

 ing the rostrum scarcely longer than the scale. This fact and 

 others leave him in considerable doubt as to the limitations of 



6 In our collection, except in one case, male specimens of P. carcinus, 

 from the shortest to those 240 millimeters long, have the short weakly 

 developed chelipeds like those of the female, but in males 250 millimeters 

 long, or longer, the chelipeds are enormously developed. 



' Fabricii Entomologia Systematica Supplementum (1798), 5, 402. 



8 Versuch einer Naturgeschichte der Krabben and Krebse (1796), 2, Tab. 

 XXVIII, Fig. 1. 



"Histoire Naturelle des Crustaces (1837), 2, 395. 



"Zool. Jahrb. Systematik (1891), 5, 701. 



"Zoologische Ergebnisse einer Reise in Niederlandisch Ost-Indien (1892), 

 2, 414. 



12 Records Indian Mus. (1910), 5, PI. XV, fig. la. Henderson and Mat- 

 thai, in the general part of their paper on palaemons, state that the rostrum 

 in the young is relatively longer than in the adults and that it is usually 

 relatively longer in females than in males. 



13 Trans. Linn. Soc. London, Zool. (1893), 5, 411. 



14 D'Ambonische Rariteitkamer (1741), PI. I, fig. B. 

 "Arch. f. Naturgesch. (1868), 5, 35. 



