96 



Records of the Indian Museum. 



[Vol. X, 



Hippolyte ventricosus, H. Milne-Edwards. 

 Plate II, figs. 1-3. 



1837. Hippolvte veiitricosus, H. Milne- Edwards, Hist. nat. Crust., II, 



P-37I- 

 1878. Vii'biiis niossambiciis, Hilgendorf, Monatsb. Akad. Wiss. Berlin, 



p. 836, pi. iv, Hg. I. 



This species is very closely related to Hippolyte varians, 

 Leach, and should perhaps be regarded merely as a subspecies. 

 The two forms may be distinguished by the following charac- 

 ters : — 



H. ventricosus. 



Rostrum rather more slender ; 

 armed with one or two dorsal 

 teeth in its proximal third ; 

 apex acuminate (fig. i). 



Antennal scale not more than 

 three times as long as broad 

 (fig- 2). 



Thoracic appendages propor- 

 tionately stouter ; middle carpal 

 segment of second peraeopods 

 as broad as long (fig. 3). 



Sixth abdominal somite 

 about one and a half times as 

 deep as long. 



Size smaller, ovigerous fe- 

 males not exceeding 20 mm. in 

 length. 



H. varians. 



Rostrum less slender, armed 

 (usually) with only a single 

 dorsal tooth in its basal third ; 

 a small dorsal tooth nearly al- 

 ways present close to apex, 

 giving it a bidentate appear- 

 ance. 



Antennal scale three and a 

 quarter to three and a half 

 times as long as broad (fig, 4). 



Thoracic appendages propor- 

 tionately more slender ; middle 

 carpal segment of second perae- 

 opods nearly twice longer than 

 broad (fig. 5). 



Sixth abdominal somite twice 

 as deep as long. 



Size larger, ovigerous females 

 sometimes 31 mm. in length. 



Apart from the characters afforded by the rostrum, which, 

 owing to the enormous range of variation that exists in both 

 species, must necessarily be somewhat inconclusive, the principal 

 difference between the two forms rests in the stouter build of that 

 found in the Indo-pacific region. Structural distinctions of this 

 nature are found in almost every part of the body, but in most 

 cases they are so slight that it is scarcely possible to demonstrate 

 them mathematically. They are, however, clearly shown in the 

 proportions of the last abdominal somite and carpal segments of 

 the second peraeopods and find less well-marked expression in the 

 form of the antennal scale. The three segments composing the 

 carpus of the second peraeopods have the same longitudinal pro- 

 portions as in H. varians. The mouth parts of the two species are 

 in closest agreement (the mandibles are nearly identical in struc- 

 ture) and no noteworthy differences are to be found in the 



