5i 



basal portion of this incurvate part is broad, while its terminal portion is moderately or very 

 narrow (f. inst. PI. V, figs. ie, 2g, $g, 4/), and it lies obliquely or nearly transversely on the 

 inner side of the pleopod, in the main or wholly beyond the fixed part of the petasma. The 

 result is that when the animal lies on the right side, thus turning the left side upwards, it 

 is impossible to see half or more than half of the petasma of left pleopod, as both its 

 broad proximal part and its terminal more or less narrow portion is covered by the peduncle 

 of the pleopod. As the shape of the narrow portion of the petasma is of the highest import'ance 

 for determining the species, and this ought to be possible without damaging the specimen by 

 cutting off one of the pleopods of first pair, I may advise the student to place the male in 

 some drops of water on an object glass so, that its right side is turned upwards, and then 

 with a needie to discard the first right pleopod backwards or forwards, so that the inner side 

 of left petasma and especially its narrow part is freely seen from above, and then to look 

 on its shape under a magnifying power of 140 or 150 times. When one has acquired some 

 experience, an examination of this simple kind will be sufficiënt for determining instantly every 

 adult male in comparing the shape of the narrow portion of the petasma with my figures. But 

 when an investigation of the whole structure of this narrow portion shall be undertaken it is 

 necessary to remove the pleopod, partly unfold the petasma so that its narrow portion is directed 

 considerably forward or nearly parallel with the pleopod (PI. IV, figs. 6g and je; PI. V, fig. \ni), 

 and undertake a partial dissection of the narrow portion under a simple microscope magnifying 

 about ióo times. 



In comparing the petasma with those in Sergestes or Sicyonella great differences are seen. 

 Of the three main-parts observed in these genera two, viz. pars externa and pars astringens, 

 are completely wanting in Lucifer, while pars media, which in Sergestes, Sicyonella and Acetes 

 is fixed by a somewhat short, proportionately narrow stalk, has in Lucifer no such stalk, but 

 an extremely broad basal pars lying flatly on the inner side of the pleopod. The narrow 

 terminal portion answers to the distal third or two-fifths of pars media in Sergestes. In all species 

 of Lucifer the narrow portion constitutes a kind of sheath open on the side and enclosing a 

 well chitinized element {pv. in many figures on Pis. IV and V) which I think is homologous 

 with processus ventralis in Sergestes and most species of Acetes. In two species, L. Faxonii and 

 L. Hanseni, this process is shaped as a long, acute needie (PI. V, figs. 3/2 — 32', figs. \n — 4.0); 

 in L. penicillifer it is broader (PI. V, figs ii — -2k), distally shaped as an oblong, concave lamella 

 with its bifid end adorned with numerous short chitinous threads, so that a bipartite brush is 

 formed. In L. interniedius processus ventralis is a narrow, robust plate (PI. V, figs. if — ig, pv.) 

 distinctly widened near the end which is deeply cleft. In L. typus and L. orientalis the same 

 process is a somewhat broad plate (PI. IV, figs. 6/2 and 6k, figs. 7/ — jg, pv.) with its distal 

 half widened and cleft by a long and deep incision differently shaped in the two species. The 

 sheath is rather simple in L. Faxonii and L. Hanseni, where it is oblong conical, somewhat 

 curved (PI. V, figs. i,g — 3/2, figs. \m — \n) with the end more or less acute, and its side opposite 

 the base is well chitinized (ch.), while the proximal side is so membranous that it is easily 

 overlooked. In L. penicillifer the membranous part (PI. V, figs. 2g — 2/2, ?u.) of the sheath 

 shows an angle and is not easily perceived ; the distal part of the sheath is well chitinized 



