ix, d, 4 Coivles: Palaemons of the Philippine Islands 331 



is no evidence that the number of the teeth increases with the 

 age. In the large majority of both males and females the 



formula is -z-r — ^r-. The dorsal border of the rostrum in young 

 9 to 10 



males and females may be divided into a proximal two-thirds 

 armed with 9 "or 10 teeth and a distal one-third usually un- 

 armed, except near the tip where there may be 2 or 3 teeth. 

 (A similar condition has been described by von Martens 16 for 

 Palaemon carcinus from Luzon.) The bases of the first and 

 second teeth and part of the base of the third tooth lie back 

 of the orbit. These teeth are more widely separated from one 

 another than the following 6 or 7 teeth, and also the ninth 

 and tenth teeth are separated somewhat more from the teeth 

 directly back of them. The unarmed portion of the distal one- 

 third has a length of 9 or 10 millimeters in specimens measuring 

 115 millimeters in body length, and beyond this lie the 2 or 

 3 rather widely separated teeth of the tip region. The usual 

 9 or 10 teeth of the ventral border are more widely separated 

 toward the tip than at the proximal end. In middle-aged males 

 and females the arrangement of the teeth is similar, but the 

 unarmed space is, relatively, slightly shorter. The bases of 

 the first, second, and third teeth of the upper border in the 

 largest males lie back of the orbit, and the unarmed space is 

 proportionately shorter than in the middle-aged males and 

 females. 



The following facts concerning the rostrum of Palaemon 

 carcinus found in the Philippines seem clear from the study 

 of our collection: 



1. The rostrum increases in length as the body length becomes greater. 



2. In young males and females the rostrum extends much beyond the an- 



tennal scale. 



3. As the males and females grow older, the rostrum extends less beyond 



the antennal scale; this is, especially, the case in males. 



4. In old males (250 to 320 millimeters), those with the enormously devel- 



oped chelipeds, the rostrum fails to reach the antennal scale by a 

 considerable distance. 



5. The number of the teeth does not vary with the length of the rostrum, 



with the length of the body, nor with the age of the individual. 



Relative position of first antenna and rostrum. — As in other 

 palaemons, the peduncle of the first antenna fails to reach the 

 antennal scale. While it increases in length as the animal grows 

 older, it retains about the same relative proportions; that is, 

 the peduncle extends forward over about three-fifths of the 



"Ibid. (1868), 5, 35. 



