GOO On Aplierusa juiliiei {M.-EJw.). 



LXXL — Aplienisa jurinei (M.-Ediv.). 

 By Alfred O. Walker, F.L.S., F.Z.S. 



This species, which is a not iincommon inhabitant of rock- 

 pools along our coasts, has been rather unfairly treated by 

 describers. A. Boeck (Skand. Arkt. Amph. p. 348, pi. xxii. 

 fig. 6) and G. 0. Sars (Crust. Norw. Amphipoda, p. 445, 

 pi. clvii. fig. 1) describe and figure what must be regarded 

 as tlie typical form, in which the third pleon-segment is thus 

 described by the latter : — " Last pair of epimeral plates of 

 metasome forming a broadish expansion, the inferior corner 

 of which is dentiform, the superior one triangularly produced, 

 cfige of the projection quite smooth/^ Boeck's description 

 is to much the same effect. 



In looking over collections from various parts of our 

 coasts, especially those of N. Wales, I have been struck by 

 the great variability of the above segment, the hind margin 

 varying from the form described by Boeck and Sars to an 

 even curve like that of Calliopius rathkei figured by Sars in 

 the same plate (2 ep.^). A very common form has the acute 

 upper angle reduced to a more or less rounded obtuse angle 

 near the middle of the curve. This appears to be commoner 

 than the typical form in the specimens examined, and is to 

 be seen in specimens of both sexes, all ages, and from various 

 localities. 



There are also considerable differences in the antennse of 

 the males and females which appear to have escaped notice 

 hitherto. All authors agree in saying that antennse 1 are 

 shorter than ant. 2, but 1 find that in the adult males they 

 are often subequal and occasionally somewhat longer. The 

 structure of the peduncle of ant. 1 also differs greatly in the 

 two sexes, though no author has called attention to this. 

 Bruzelius and Boeck both speak of a tooth at the end of the 

 lower margin of the last joint of the peduncle, which is not 

 mentioned or figured by (i. 0. Sars ; yet both are strictly 

 correct, the former being the male and the latter the female 

 form. Further, the adult male has, in addition to this tooth, 

 from one to three teeth on the lower margins of the last two 

 joints of the peduncle, each tooth being generally crowned 

 with a calceolus, which I have never seen on the flagellum 

 in this species. These teeth are indicated in Boeck^s figure 

 of the antennse, which are shown of equal length. 



An adult male with the rounded or subangular form of the 

 hind margin of the third pleon-segment might well be taken 



