ON THE LYSLANASSA MAGELLANICA ETC. 17 



on the former, and highest on the outer branch (a): This branch has at 

 its point a spine, separated by a suture, and may by this be distinguished 

 from the inner (b), which is moreover somewhat shorter and broader. 



The tail-feet of the last or 6 th pair (Fig. 20, right foot) are shor- 

 ter, broader and more moveable. Their length is 8 millim. The stem is 

 almost rhomboidal, with the lower external angle projecting acutely. The 

 external terminal branch (a) is also somewhat longer than the internal (b) and 

 has also a detached spine at the point. Both branches have about the 

 same shape, are tolerably thin, though thicker at the outer edge, of a 

 broad lancet form, and are provided with numerous bristles on the inner 

 border. Also the stem has similar bristles on its inner border and at the 

 outer and lower acute angle. These feet stretch somewhat behind the 

 ends of the other tail-feet and even somewhat further back than the 7 ,h 

 tail-segment. 



The 7 h tail-segment or, as it is called, caudal appendage (fig. 21) 

 is of considerable size, extending almost to the ends of the last tail-feet. 

 Its length is 6 millim. It is forked a little below the middle, and the ope- 

 ning between the two halt's somewhat wider towards their termination. It 

 is tolerably thick with a blunt ridge which on both sides goes parallel with 

 and close beside the external edges of the lobes, with a hollow along the 

 middle between the base and the opening. The lobes are brought up 

 smoothly to points, and are destitute of the moveable spines at the end, 

 and no spines are visible on their sides. 



The Group of the family Gammaridae, which the subfamily Lysia- 

 nastina constitutes, seems to be tolerably natural and well defined, but it 

 happens with it, as with many other natural groups, e. g. Felidae among 

 mammalia, Ct/prinidae among fishes, etc., that the forms belonging to it, 

 especially the different species within the same genus, not unfrequently pre- 

 sent such slight differences, that it requires a very minute examination to 

 distinguish them. This group is distinguished by the form of the tipper 

 antennae and mandibular, the former having a peculiarly thick shaft of which 

 the two last joints are very short, and the latter a more or less sharp edge 

 with few or no teeth (fig. 52), and the inner process (a) — processus ac- 

 cessorius, Bruzelius — little or sometimes not at all developed. To this 

 may be added that the 2 nd pair of truncal feet are very long and slender, 

 having in general a very small claw r , which however is in one instance absent. 



Nova Acta Reg. Sue. So. Ops., I lie SSrie. 3 



