LONO NAMES FOE SHORT LARV^ 221 



in the JUwphausice, while on the contrary it is very frequent 

 among the Peneeidas.' 



Family 2. Sergestidce. 



The branchial system is impoverished or lost, the 

 epipodal plates and podobranchial plumes, when present, 

 being restricted to rudimentary structures on the second 

 maxillipeds. The first pair of trunk-legs, and some- 

 times the second, are simple, the chelge of the third are 

 minute, the fourth and fifth pairs are feeble, rudimentary, 

 or absent. 



The genera assigned to the family are Sergestes, Milne- 

 Edwards, 1830 ; Acetes, Milne-Edwards, ISoCT; Petalidium, 

 Sp. Bate, 1881 ; ScicMwris, Sp. Bate, 1881 ; and Lucifer, 

 Vaughan Thompson, 1829, a pre-occupied name altered 

 to Leucifer by Milne-Edwards in 1837. A very few re- 

 marks must suffice on the discrimination of these genera. 

 In Sergestes the last two pairs of trunk-legs are rudi- 

 mentary, in Acetes the last but one is reduced and the last 

 is wanting, in Leucifer both pairs are absent. In Sergestes 

 the arthrobranchias are wanting, in Petalidium they are 

 found on the second and third maxillipeds and the first 

 three pairs of trunk-legs. In Sergestes, Professor Smith 

 remarks, the branchia? are compound phyllobranchiae, 

 while those of Pencens in the preceding family are com- 

 pound trichobranchias. 



The larval forms of Sergestes have been partitioned into 

 genera and species. The youngest form known is desig- 

 nated JElaplwcaris by Dohrn (see Plate IX.) ; another, and 

 presumably later form, is called Platysdcus by Bate ; this is 

 followed by Acanthosoma, Glaus, and that by Mastigopus 

 of the same author. The species known as adults are 

 very numerous, of very various sizes, from many differing 

 localities, Sergestes atlanticus, Milne-Edwards, being found 

 both in the Mediterranean and in the Atlantic from 

 Greenland to the tropics. The account of the genus occu- 

 pies eighty-eight quarto pages and seventeen plates of 

 Spence Bate's ' Report on the Challenger Macrura.' It 



