404 M. A. Boeck on the Amphipoda 



furnished on the upper surface with about twenty erect seti- 

 gerous tubercles. The flagellum consists of from thirty-four 

 (females) to forty-two (males) joints. The second joint of the 

 palpi of the maxillipedes is shorter than in E. cuspidatus, and 

 wants the teeth which characterize the latter. The hands of 

 the first pair of legs are of the same form as in E. cuspidattis, 

 but rather rounder, and not so oval ; the three posterior pairs 

 of thoracic legs are very long ; the fifth joint is nearly as long- 

 as the preceding two together, whilst it is considerably shorter 

 in cuspidatus. The outer branch of the fifth pair of abdominal 

 feet is only a little more than half as long as the inner one, 

 and the telson is less cleft than in cuspidatus. 



Iduna, mihi. — Bruzelius described a Gammarus brevicomis 

 from the Norwegian coast in general and from Bohuslehn ; 

 and Prof. Sars found a species in Finmark, which he named 

 Gammarus fissicornis. Both species must be separated from 

 the genus Gammarus, and placed under a new genus nearly 

 allied to Eusirus. The secondary flagellum, which in the 

 latter is very short, becomes extremely long in the two species 

 above mentioned, whilst the flagellum itself is short. The 

 inferior antenna? are short and nearly subpediform. The mas- 

 ticatory tubercles of the mandibles are small ; and the inner 

 lamella of the first pair of maxilla?, as in Eusirus, is oval, and 

 furnished with isolated ciliated seta?. The masticatory lamella? 

 of the maxillipedes are small, and their palpi are much elon- 

 gated. The first two pairs of legs are furnished with strong 

 prehensile hands ; their fourth joint emits from its inferior 

 posterior angle a strong process, as in Leucothoe ; the following 

 pair of legs are very thin and long ; the last pair of legs are 

 very long ; the abdominal feet are long, and the telson deeply 

 cleft. The first epimera are strong, larger than the following- 

 ones ; they consequently show much agreement with Eusirus, 

 and differ greatly from the typical species of Gammarus. The 

 two species may be easily distinguished from one another by 

 their different size, and also because the second and third seg- 

 ments in Iduna fissicornis are produced behind into a spine, 

 whilst in the other they are smooth. 



The ovigerous lamella? are of somewhat different size in this 

 group. In Leucothoe and Iduna they are small, and the re- 

 spiratory lamella? long and broad ; in Eusirus the ovigerous 

 lamella? are broader than in the preceding ; and this is still 

 more the case in Stenothoe. In Leucothoe and Stenothoe there 

 is no secondary flagellum on the superior antenna? ; in Eusirus 

 it is small, and in Iduna long. The mandibles are destitute 

 of palpi and masticatory tubercles in Stenothoe ; in Leucothoe 

 they have palpi, but no masticatory tubercles, which are small 



