348 THE VOYAGE OF H.M.S. CHALLENGER. 



" And very similar to that of Sergestes is the development of Leucifer. Here the 

 earliest Zoea of a species from the Western Pacific has at first no eyes, then sessile ones 

 come out, and the animal then presents the form which Dana has called Ericthina 

 demissa, and which Claus suspected to be not a Stomatopod but a Schizopod larva. 

 After the second moulting this Ericthina gets stalked eyes and very long setae on all 

 its appendages, becoming a rather long, very delicate Zoea. It now enters the Amphion 

 stage, but never gets more than four pairs of pereiopods, and loses another pair of these 

 when it moults for the youngest Leucifer stage, in which two pairs of pereiopods are 

 absent. 



"The next question, after having found this out, was, of course, whether Amphion, 

 Sergestes, and Leucifer, leave the egg as a Zoea, or whether there is a preceding Nauplius 

 stage. My own impression is that in the two first-named genera this is not the case, as 

 the youngest Zoeas which I caught had all the same size, and as none of them was 

 without the large lateral stalked eyes. As for Leucifer, the question appears to me to be 

 doubtful ; l for it is, from what I have seen, quite possible that my youngest Zoea, which 

 has only got a central eye, may be preceded by a Nauplius. Of course the simplest 

 thing would be to get the eggs ; but there is the difficulty, for Amphion is caught very 

 rarery, and has never been obtained at any other time but between 8 and 12 p.m., when 

 it is extremely difficult by lamp-light to find out the youngest stages. Sergestes larvas 

 are commoner, appearing also in the day-time, and Leucifer is sometimes caught in 

 abundance. I hope, therefore, that I shall succeed in completing my researches about 

 this question, especially as far as the latter two genera are concerned. 



"H.M.S. 'Challenger,' Honolulu, Sandwich Islands, July 30, 1875." 



Petalidium, 2 Spence Bate. 



Petalidium, Sp. B., Ann. and Mag. Nat. Hist., ser. 5, vol. viii. p. 194, 1881. 



External tissue membranous. Carapace about one-third of the length of the animal, 

 dorsally elevated above the frontal region to a laterally compressed crest, and anteriorly 

 produced to a small point. The cervical fossa is well defined. The rest of the animal is 

 smooth. Pleon with the somites subequal, the fifth being a little shorter than those 

 anterior to it, and the sixth somewhat longer. 



The ophthalmopoda are uni-articulate, long, subcylindrical, and slightly compressed, 

 and stand upon their own somite, which projects between them in advance of the frontal 

 margin. 



First pair of antennae with the first joint excavated on the upper surface, and 



1 This has since been cleared up by Professor Brooks (Phil. Trans., pt. i. p. 57, 1882), who has shown that the 

 brephalos of Leucifer is in the Nauplius-stage. 



2 iitrctXiiiou, a small leaf. 



