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P. semisulcatus : the only differences seem to be the following. In Alcock's inoiiodoii the cervical 

 groove, above the hepatic spine, appears in his figure i shorter than in P. scmimlcatus, in which 

 it extends upward to beyond the middle of the distance between the hepatic spine and the 

 upper border of the carapace-, in P. semisulcatus the ridge that, from the hepatic spine, above 

 and parallel with the post-antennular crest, runs obliquely forward and upward, is rather long, 

 much longer than in Alcock's figure i and in the description this ridge is also described by him 

 as short. In the third place the petasma shows a somewhat different form. In the largest of 

 the "Siboga" specimens, long 175 mm., from Stat. 213, the petasma closely resembles that of 

 P. ashiaka Kish. (Kishinouye, 1. c. PI. VII, Fig. 4), which species is identical with P. semi- 

 sulcatjis\ in Alcock's figure \a, however, the distal extremity of the petasma appears concave 

 and it ends proximally in one median process, in P. semisulcatus^ on the contrary, in two 

 lateral processes. For the rest his description of P. mouodon perfectly well accords with the 

 specimens of P. semis2(lcatus that are lying before me. /\s the Japanese P. semisulcatus occurs 

 not only in the East Indian Archipelago, but also in the Red Sea, as I already pointed out, 

 this species no doubt also occurs in the Bay of Bengal and along the coasts of India, a reason 

 the more for regarding Alcock's monodon as identical with the species of de Ha.^n. In Bate's 

 figure I , that is a good figure of P. semisiilcatns, the grooves and ridges on the sides of the 

 carapace, anteriorly, have been quite exactly figured. 



The male from Stat. 121 is 90 mm. long. The rostrum that reaches just beyond the tip 

 of the antennular peduncle, projects straight forward and is --dentate, the second lower tooth 

 is implanted just below the foremost tooth of the upper margin as in figure i of Alcock's 

 Monograph and the post-rostral carina is deeply grooved. The fourth abdominal somite is 

 carinate in little more than half its length. The external maxillipeds reach to the middle of 

 the antennal scale, while the third legs extend to the apex. 



The female from the same Station is 85 mm. long. The rostrum, that reaches also just 

 beyond the tip of the antennular peduncle, is ^-dentate, its acute tip is slightly turned upward ; 

 the first or posterior tooth of the lower margin is situated just below the foremost tooth of 

 the upper, so that two teeth of the lower margin stand in advance of the former. The fissure 

 between the two lobes of the thelycum is still somewhat broader than in the adult female. In 

 both specimens from Stat. 1 2 i the flagella of the lower antennae show the beautiful coloration, 

 characteristic of P. ashiaka (Kishinouye, 1. c. Plate III), of which neither Spence Bate nor 

 Alcock make mention. 



The male from Siau Island is 76 mm. long. The rostrum fully resembles that of the 

 female from Stat. 121, but it does hardly reach to the tip of the antennular peduncle. The 

 larger female is 95 mm. long. The rostrum fully agrees with that of the male, but the tip is 

 more clearly turned upward. The carina on the fourth abdominal somite extends only to the 

 middle of the tergum. The rostrum of the other female, which is 52 mm. long, also resembles 

 that of the male. The two lobes of the thelycum are here separated by a broad interspace. 

 In these three .specimens the coloration of the antennal flagella has faded away. 



The rostrum of the largest male from Stat. 213 is straight, not at all upturned at its 

 extremity, and hardly reaches beyond the penultimate joint of the antennular peduncle. The 7 



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