KONGL. SV. VET. AKADEMIENS HANDL1NGAR. BAND. 22. N:0 7. 65 



«coupling spines» recorded by Stebbing, called »les epines particulieres» by G. 0. Saks; 1 ) 

 the anterior one of these spines is the longest, armed along the hind margin with six retro- 

 verted teeth, the shorter spine has five teeth. The lower parts of the peduncles show 

 distinctly that hexagonal plating of the hypodermis alluded to above, p. 61. The rami 

 of the first pair consist each of twelve joints, the first joint is more than half as long as 

 all the following joints together; on the inner ramus it carries a stout bristle, cleft at the 

 apex, it is the »cleft spine» mentioned by Stebbing 1. c. p. XIV 2 ) or »la soie particuliere a 

 bout bifurque» of G. 0. Sars 1. c. p. 133; this cleft bristle is feathered, but less densely 

 than the other setae. Above the cleft bristle there are some tufts of short, fine hairs. 



The urns has the first segment a little shorter but broader than the coalesced 

 second and third. 



The uropoda (PI. V, fig. 22). The peduncle of the first pair is narroAv, linear, 

 shorter than that of the second pair, and shorter than the inner ramus: it has a short 

 spine just below the middle of the inner margin, and another one at the lower corner. The 

 inner ramus is twice as long as the outer, and much broader at the base, the outer margin 

 is finely serrated, the inner margin is less distinctly serrated; the outer ramus is very 

 narrow, almost styliform, the inner margin is serrated, the outer smooth. The peduncle of 

 the second pair is narrow, linear, shorter than the inner ramus, the margins are smooth. 

 The inner ramus is very narrow, elongated, scarcely a third longer than the outer ramus, the 

 outer margin is smooth, the inner finely serrated; the outer ramus is almost as. broad at 

 the base as the inner one, tapering; the outer margin is smooth, the inner finely serrated. 

 The third pair have the peduncle shorter than the last ural segment, very broad, almost 

 twice as broad as that of the first pair; the peduncle is much shorter than the inner ramus, 

 and a little shorter than the outer. The inner ramus is much broader at the base than 

 the outer one, tapering, serrated on both margins; the outer ramus is more than half as 

 long as the inner, smooth on the outer margin, and finely serrated along the inner margin. 



The telson is more broad than long, rounded behind, scarcely longer than half 

 the breadth of the peduncle of the last pair of uropoda. 



x ) G. O. Sars. Histoire naturelle des Crustaces d'eau douce de Norvege. I, p. 53 and 133, pi. 5, 

 fig. 8' and 8". 



2 ) I had totally overlooked the existence of the "coupling spines» and the »cleft spine» of the pleopoda 

 until I read about them in Stebbing's work on the Cballenger-Amphipoda. He says 1. c. p. XIV: »Among the 

 Gammarina occasionally these spines (coupling-spines) are numerous; among the Hyperina there are rarely, norm- 

 ally perhaps never, more than two to each peduncle. In both groups they are clearly spines that have been 

 modified to serve one and the same purpose, namely to hold the peduncles together for the swimming-stroke. 

 For this purpose the apex of each spine is blunted and has backward directed teeth, the edges also often having 

 a retroverted serrature, so that the spines of each pair of peduncles can be interlocked. That both groups, not- 

 withstanding their otherwise extremely divergent forms, should so universally possess these coupling-spines, is 

 surely a note of common ancestry. It is also easy to see that two quite simple spines in this position might be 

 of some service for the object in view by the effect of mere friction, while natural selection would be ready to 

 avail itself of any variation in the direction of the roughening of the spine, until the strongly serrate edges and 

 dentate apices had been at length evolved. In the branches of the pleopods we find another note of community 

 of origin for the two groups above mentioned. Besides the obvious similarity which these branches display in 

 almost all the genera and species, they have in common the less easily noticed feature of carrying one or more 

 cleft spines (see G. O. Sars, 1. c), on the inner margin of the first joint of the inner branch. To this there are 

 only rare exceptions, and those, perhaps, not difficult to explain. Throughout the Hyperina it appears that the 



K. St. Vet. Ak. Handl. Band. 22. N:o 7. V 



