REPORT ON THE CRUSTACEA MACRURA. 457 



The second pair of gnathopoda resembles the first in form, but is longer and more 

 important. 



The pereiopoda consist of four pairs and are all formed on the same plan as the 

 gnathopoda, which they closely resemble ; the posterior pair, according to Suhm's 

 drawing, has only three joints belonging to the primary division, instead of four, as all 

 the others have. 



The pleon consists of six somites and the telson. 



The pleopoda are in a rudimentary condition, but the sixth pair is well developed 

 and helps to form an efficient rhipidura. 



The telson is long, and armed at the sides and extremity with six or eight stiff hairs, 

 the posterior of which have slightly serrate edges. 



In the West Pacific Ocean a specimen (PI. LXXXV. fig. 2) was taken of a species 

 that corresponds with the genus Sceletina of Dana, but which Professor Brooks has 

 shown to be the young of Lucifer, corresponding with the Acanthosoma-stage of 

 Sergestes. 



Our specimen is about 1*5 mm. in its entire length, of which the carapace is 0'4 mm., 

 or about one-fourth of the whole length of the animal. 



The frontal margin of the carapace is produced to a flat sharply pointed rostrum, 

 whence it recedes in a concave line to the fronto-lateral angle, which is anteriorly pro- 

 duced to a strong sharp point, from which the lateral margin recedes in a waved fine 

 to the posterior extremity of the pereion. 



The pereion is enclosed within the carapace, and the pleon consists of six somites 

 and the telson ; the anterior five somites are subequal in length, and are inferiorly pro- 

 duced to a point on each side ; the sixth somite is rather more than twice the length of 

 either of the preceding, and is posteriorly produced on the dorsal surface to a strong 

 point. 



The telson is about two-thirds the length of the preceding somite. 



The ophthalmopoda are pyriform and about twice the length of the rostrum. 



The first pair of antennse is about twice the length of the ophthalmopoda, and the 

 second pair is about half the length of the first. 



The oral appendages were not examined, but Professor Brooks has examined 

 them in a slightly older form ; the mandibles are still without the synaphipod that is so 

 conspicuous in the adult ; the pereiopoda, which consist of four pairs, are biramose and 

 correspond in form to those of the Acanthosoma of Sergestes. 



The pleon is yet without any appendages excepting the posterior pair which forms 

 part of the rhipidura, which is biramose and foliaceous, but does not exceed the telson in 

 length. 



(ZOOL. CHALL. EXP. — PART LTI. — 1887.) Fff 58 



