350 The Philippine Journal of Science wu 



The specimens of Palaemon philippinensis in our collection 

 bring out the following facts concerning the rostrum in this 

 species : 



1. The rostrum increases in length as the body grows longer. 



2. Its relative length compared with the length of the antennal scale 



becomes less with increasing age, and only in the young does it 

 extend beyond the tip of the scale. 



3. The convexity of the dorsal border over the eye increases as the indi- 



viduals grow more mature, and as a result the distance between the 

 longitudinal ridge on the side of the rostrum and the dorsal border 

 increases greatly. 



4. The wide spacing between the teeth near the tip of the rostrum decreases 



with age, and almost disappears in old males. 



Relative position of first antennas and rostrum. — The peduncle 

 of the first antenna retains the same relative proportions with 

 reference to the antennal scale of the second antenna throughout 

 life, and never extends to the tip of the scale. Generally in 

 young and middle-aged males and females the peduncle of the 

 first antenna extends to about the third or fourth tooth of the 

 lower border of the rostrum, but in the largest specimens, espe- 

 cially the males, it reaches or almost reaches the tip of the 

 rostrum. Small males which have taken on the mature male 

 characteristics (young mature males) also sometimes show the 

 tip of the peduncle even with the tip of the rostrum (Table II, 

 No. 13). The relative position of the tip of the rostrum and 

 the tip of the peduncle of the first antenna at different ages 

 reminds one of the condition in the local form of Palaemon 

 carcinus, although in a series of Palaemon philippinensis ar- 

 ranged according to increasing body length the approximation 

 of the tips of the peduncle and rostrum does not take place so 

 gradually and uniformly with increasing body length as in the 

 former. 



First pair of legs. — In the smallest males and females a portion 

 of the propodus extends beyond the tip of the antennal scale, 

 while in larger males and females a portion of the carpus is 

 also seen extending beyond it (Table II). 



Chelipeds. — The chelipeds of small males and females are 

 shorter than the body, and with certain exceptions this condi- 

 tion persists with increasing body length, although the chelipeds 

 of larger individuals show a relatively greater length compared 

 with that of the body (Nos. la, 2, 5, 7, 8, 9, 10, 12, 14, 16, 17, 18, 

 19, 20, 21, 22, 25 ( ?) , 32, 33, 34, 35, 36, 37, 38, 39) . The excep- 

 tions mentioned are the large mature males (Nos. 26, 27, 28, 29, 

 30, 31) and the smaller males which have taken on the mature 

 characters (Nos. 3, 4, 6, 11, 13, 15, 23, 24). By mature charac- 



