330 The Philippine Journal of Science 1914 



the species, and he is forced to regard such species as belonging 

 to a variety in which the apical growth of the rostrum has 

 been arrested. It does not seem to me probable that the 

 gradual decrease in ' length between the tip of the anten- 

 nal scale and the tip of the rostrum, which is so strikingly 

 illustrated in our series, is unique for the form we have 

 here in the Philippines. On the contrary, I believe that an 

 examination of a large series of P. carcinus from India 

 will show a similar condition, and I am inclined to agree with 

 that part of Henderson's statement in which he says that the 

 apical growth of the rostrum may be arrested. From a study 

 of specimens of Palaemon carcinus and Palaemon philippinensis 

 sp. no v., I believe that the growth of the rostrum becomes 

 partially arrested when the so-called mature characters are 

 acquired and that this change is especially marked in the males. 



Curvature and dental formula of rostrum. — Females of all 

 ages show the distal one-third of the rostrum curved upward, 

 but this is more evident in the young than the old. The arching 

 over the eye, which is pronounced in Palaemon carcinus from 

 India, is not conspicuous in the Philippine form, and remains 

 about the same throughout the life of the female. The upward 

 curve of the distal part of the rostrum in the males does not 

 seem to differ from that in the females, except in the large 

 males (those with the enormously developed chelipeds), where 

 the tip scarcely bends upward at all. The degree of arching 

 over the eye is slightly greater in the old than in the young 

 males. 



The dental formula is very variable. An examination of 

 the specimens in the collection shows the formula for the males 



(100 to 320 millimeters) to be ^ f'! 8 ' 14 In one exceptional 



o, y, iu, 11 



case 12 teeth are found on the lower border, 2 of which, how- 

 ever, are situated well up under the arch over the eye. The 



12 

 smallest male (100 millimeters) has the formula -^-, while the 



o 



largest male (320 millimeters) has -^-. In the females (115 



11 1? 13 



to 250 millimeters) the formula is * ' tr'-Tn - Th °se of the smallest 



o, y, iu 



12 

 (115 millimeters) and largest (about 250 millimeters) are ^ 



12 

 and -jT-, respectively. It appears that the number of teeth in 



the males is somewhat greater than in the females, but there 



