ix, d, 4 Cowles: Palaemons of the Philippine Islands 325 



of this series with individuals of the Indian species shows 

 certain distinct and constant differences. The local form differs 

 slightly from typical P. carcinus in the shape of the rostrum, 

 the rostral formula, the arrangement of the teeth on the rostrum 

 at all ages, and the position of the tip of the rostrum with 

 reference to the tip of the antennal scale at different ages ; there 

 is, however, a close similarity in the shape, armature, and 

 proportions of the segments of the chelipeds. The characters 

 of the chelipeds, just mentioned are of great diagnostic value 

 in determining species of the genus Palaemon, and for this 

 reason I have not described it as a new variety. It should be 

 mentioned, however, that our local form of Palaemon carcinus 

 probably closely resembles a form originally known as Palaemon 

 rosenbergii de Man, 2 but which is now considered by de Man, 3 

 Ortmann, 4 and others as a variety of P. carcinus. The original 

 description of P. rosenbergii was based upon a single full-grown 

 female, and as no male has been seen I shall not place our 

 local form under de Man's variety. However, his description 

 agrees closely with a female specimen of about the same size 

 which is in our collection. The shape, size, and toothing of 

 the rostrum, as well as the measurements of the chelipeds, 

 are almost identical. 



The detailed description of the Philippine form of P. carcinus 

 which follows is considered advisable, because our form differs 

 from the type, because our collection affords a large number 

 of different ages and sexes, and because it is the most important 

 species from a commercial point of view in the Philippine 

 Islands. 



Rostrum and antennal scale. — An examination of 21 female 

 specimens, varying in body length 5 from 115 to 250 millimeters, 

 shows with one exception that the rostrum extends beyond the 

 antennal scale. This exception (230 millimeters long) has a 

 rostrum which appears to be normal, but the tip just reaches 

 the distal end of the scale. In the largest specimen (250 milli- 

 meters), however, the tip extends slightly beyond, while in a 

 young female (115 millimeters) the rostrum extends one-fourth 

 of its length beyond the end of the antennal scale. Thirty-six 



1 Notes Leyden Mus. (1879), 1, 167. 



3 Zoologische Ergebnisse einer Reise in Niederlandish Ost-Indien (1892), 

 2, 417. 



'Zool. Jahrb., Systematic (1891), 5, 701. 



By body length, or length, is meant the distance from the tip of the 

 rostrum to the tip of the telson. 



