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



the petasma on the first pair of pleopoda is slightly enlarged, and there are three small 

 teeth or points attached to the lateral margins of the sixth somite of the pleon, the 

 central tooth assuming a larger proportion to the others ; but the telson still retains the 

 simple condition of the female. 



On the same plate, fig. 4 represents another specimen, about 7 mm. in length, that 

 was taken in the tropical part of the Atlantic. This agrees with fig. 2 in most 

 points, and is probably the same stage of a different species ; it has, however, lost 

 the minute denticle nearest to the posterior angle of the sixth somite, and apparently 

 retained the larger one anterior to it ; it has also lost the small denticle in front of the 

 latter, but further in advance is a small process that appears to be a future tooth ; so that 

 we see in an incipient stage the gradual production of the two small teeth that appear 

 to be the constant condition of the males in the species of this genus. The telson still 

 retains its smooth condition. 



AVhether these several specimens belong to one species or not, it is difficult to 

 determine, but as all species pass through similar stages that resemble each other as far 

 as external evidence enables us to decide, it is most probable that these are derived 

 from the two forms Lucifer typus and lAicifer reynaudii, which appear to live closely 

 associated together. Dana, speaking of Lucifer reynaudii, says '}■ — 



" In one male about half grown, the anterior tooth of the sixth segment of the 

 abdomen was obsolete, and the posterior spine was quite short, although of the same general 

 character as to its extremity, as in full grown males. This intermediate character in an 

 immature male seems to confirm our inference, drawn from the general identity of 

 character and their frequent association, that the animals described as such are actually 

 male and female." 



Geographical Distribution. — The genus appears to range all over the tropical and 

 subtropical regions of the Atlantic and Pacific Oceans, within a hundred fathoms of the 

 surface, but according to Professor Brooks they are abundant on shallow shores. 



Lucifer typus, Vaughan Thompson (PI. LXXXIIL). 



Lucifer typus, Vaughan Thompson, Zool. Researches, p. 58, pi. vii. fig. 2, 1829. 

 Leucifer typus, Milne-Edwards, Hist. Nat. Crust., t. ii. p. 469. 

 Lucifer typus, Faxon, Chesapeake Zool. Lah., 1878, p. 113. 



„ pacificus, Dana, U.S. Explor. Exped., Crust., p. 673, pi. xlv. fig. 2 (young). 



Male. — Antennal somite one-fourth the length of the animal, measured from the 

 frontal margin to the extremity of the telson, and rather more than twice the length of 

 the carapace. 



The anterior five somites of the pleon are subequal in length, the first and fifth 



1 U.S. Explor. Exped., Crust, vol. i. p. G73. 



