348 The Philippine Journal of Science 1914 



(33.5 millimeters) ; in specimens from 90 to 96.5 millimeters long 

 the tip of the rostrum barely reaches the tip of the antennal scale ; 

 in those from 96.5 to about 124 millimeters long the rostrum 

 usually fails to reach the tip of the antennal scale by from 1 

 to 3 millimeters; and in specimens from 124 to 144 millimeters 

 long this distance usually increases to from 4 to 6 millimeters. 

 The specimen (111.5 millimeters) indicated in Table II is a male 

 which has assumed adult male characters (young mature male), 

 although its body is still only of medium length. It is covered 

 with a dirty brown sediment, and its chelipeds are enormously 

 developed relative to the body length. The rostrum fails to 

 reach the antennal scale by 7.5 millimeters. The chelipeds, al- 

 though much shorter than those of the specimen 144 millimeters 

 long (Table II), are almost perfect miniatures, showing prac- 

 tically the same proportions. While the decrease in the relative 

 length of the rostrum with reference to the antennal scale is 

 not so regular with increasing size as in the local form of 

 Palaemon careinjis, it is, nevertheless, plainly apparent. 



Curvature and dental formula of rostrum, — Specimens of dif- 

 ferent ages show such a remarkable difference in the shape of 

 the rostrum, that if I had not seen all of my specimens when 

 alive I should hesitate to consider them as belonging to the 

 same species. In this respect P. philippinensis reminds one of 

 the variable form of the rostrum in P. webafri de Man 27 and 

 P. dispar von Martens. 28 Certain characteristic markings men- 

 tioned under the section devoted to the color of the living in- 

 dividuals and not found in any other species in our collection 

 were present in all. The youngest males (33.5 and 39.5 milli- 

 meters) and the youngest females (47 to 71.5 millimeters) have 

 the dorsal border of the rostrum almost straight, only a very 

 slight convexity over the eye being apparent. As the "males 

 feminises" (those similar in general appearance to females) and 

 females increase in body length, the convexity becomes gradually 

 more pronounced. In the largest males it is very striking, but 

 in the largest females it is not so much so. The young and 

 middle-aged males which take on the adult characters usually 

 show a greater curvature of the dorsal border of the rostrum 

 over the eye than do the "males feminises" of the same size. 

 Correlated with this increase in the convexity, as these males and 



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

 2, 421. 



"Arch. f. Naturgesch. (1868), 5, 41. 



