152 CARL BOVALLIUS, AMPHIPODA HYPERIIDEA. I. 2. HYPERIID^E. 



Hyperia medusarum. 



fleshy joints, (the first of which is the shortest,) and by a long and curved member, terminated 

 by a nail; the six posterior legs are directed backward; the three anterior caudal segments with 

 each a pair of swimmers; the fourth caudal segment has on each side a pair of foliaceous styles 

 borne on a two-jointed cylindrical footstalk; the tail consists of two foliaceous plates, each ter- 

 minated by two smaller ones, strongly pointed and articulated to the larger; and is also furnished 

 with a second pair of lateral style process. 



This description differs from that of the Cancer Medusarum, Otho Fabrtcius, Faun. Groen. 

 N:o 232, in the number of joints of the legs, and in the four anterior being unarmed; the con- 

 formation of these legs distinguishes it also from Gammarus Medusarum, of J. C. Fabricius, of 

 which a part of the specific character is »manibus quatuor monodactylis».» 



This last remark of Sabine about the »unarmed» first two pairs of peraeopoda is 

 doubtless due to the fact that the dactyli of these pairs of legs are very small and 

 shorter than the bristles densely surrounding them and are thus easily overlooked if the 

 animal cannot be microscopically examined. In all other respects the description is quite 

 adequate, and the strange statement regarding the two-jointed peduncle of the first pair 

 of uropoda is most probably a good observation, because I have observed the same 

 feature in another member of the family Hyperiidaa, Parathemisto Goesi. In my opinion 

 it is due to the moulting process. 



From this time the species occurs in literature only as a mere citate under one 

 or other of the names quoted above until 1861 when A. Boeck rediscovered the animal. 

 He did not, however, recognise its identity with 0. F. Muller's Cancer medusarum, but 

 looked upon it as a new species, naming it Hyperia spinipes (1. c. p. 636), and distinguish- 

 ing it from H. galba (= H. Latreillei) by »the first two pairs of legs being more strongly 

 built; the fifth joint or the hand (= metacarpus) being densely set with tolerably long, 

 straight and strong bristles, and the angle of the head between the upper and lower an- 

 tennas being much larger and more protruding.)) 



In 1865 Goes 1 ), not knowing the new species of Boeck, also found the animal 

 among the Arctic amphipods and gave it as a variety of Hyperia exulans (= H. Latreillei), 

 saying: »Ad nostras oras alia etiam forma occurrit paiillum diversa, pedum primi ordinis 

 articulo quinto fere cylindrico undique setoso, ungue minuto.» I have examined his very 

 specimens and found them to be males and females of the true Hyperia medusarum, 

 0. F. Muller. 



In 1870 A. Boeck gave the following diagnosis of his Hyperia spinipes: 



»Pedes lmi paris manu ovali, spinis longis multis armata; calce perbrevi. Pedes 2di paris 

 calce parum longiore qvam apud pedes lmi paris; manu spinis longis instructa. Appendix cau- 

 dalis longior qvam lata, ad pedunculi pedum saltatorium ultimi paris tertiam partem porrecta. 

 Pedes saltatorii ultimi paris pedunculo duplo longiore qvam lato.» 



Two years later he added good drawings of the animal and the following description, 

 which I translate: 



»The length of the animal is 10 mm. The body is very similar to that of the preceding 

 species (Hyperia Latreillei). The head is, viewed from front somewhat longer and narrower. 

 The angle of the head between the upper and lower antennte is produced and broad. The first two 

 pairs of legs are more strongly built than those of the preceding species. The fourth joint (carpus) 



T ) A. Goes. »Crustacea amphipoda maris Spetsbergiam alluentis» etc. Ofvers. af K. Vet. Ak. Forhand- 

 lingar for 1865, p. 534. 



