526 Ake nordenstam 



same year two additional members of Anatanais were described: T. spongicola 

 Barnard and T. Ohlini Stebbing. In 1919 Stebbing added another species, 

 7. Nierstraszi. The subgeneric position of T. Gayi Nicolet (1849) remains un- 

 decided, the number of free abdominal segments beeing unknown. 



One of the new species of Tanais which I propose to describe, T. lineaius, 

 is remarkable for the sexual difTerence which is apparent even in immature 

 individuals. As mentioned before, no adult specimens are present, but there 

 are two kinds of young individuals, one (probably the females) more narrow, 

 almost cylindrical, with the thoracic segments longer and the ventral side con- 

 vex, the other (probably the males) broader, with the thoracic segments shorter 

 and the ventral side flat. The pairs of antennae, the mouth-parts, and the legs, 

 (also the chelipeds) agree very well in both kinds. In a great many other 

 genera (cf. HANSEN 1913) the same sexual difference is the rule, but it has 

 not before been recorded from the genus Tanais. 



Many species of Tanais are not very well known. This is especially the 

 case with the more common young individuals, which are very similar to each 

 other in different species (cf. HANSEN 191 3, VanhOffen 1914). The legs and 

 mouth-parts have but rarely been fully described but may certainly show 

 differences in all species, also in immature individuals. In conformity with 

 this opinion and emphasizing the importance of describing even immature 

 specimens, I have thought it worth while to deal with the present small amount 

 of material also, though at least 4 previously described species are so similar 

 or so imperfectly known that there is a possibility of their being identical. 

 These species are: T. gracilis Heller, Normani Richardson, spongicola Barnard 

 and Ohlini Stebbing. T. viacrocheles Nicolet, which has the anterior border 

 of the carapax truncate, may be a different species — perhaps as Vanhoffen 

 (1914) supposes a collective form. 



Tanais (Anatanais) marmoratus n. sp. — PI. 20, fig. i; text figs, i, 2. 

 Subadult male (length 5 mm) and immature specimen (length 2.5 mm). 



Loc. Juan Fernandez: Masatierra, on a buoy in Cumberland Bay. 



Description . 



Body with a length of about 5 times the width, laterally with a few setae. 



Carapax, seen from above, with the lateral margins convex to about half 

 of its length (in the immature specimen evenly convex), anterior border about 

 half as broad as posterior. Frontal margin between the eyes triangulate. Eyes 

 well developed, of about 6 ocelli, on conical peduncles, which are situated in 

 small cavities. 



Thoracic segments with the lateral margins rounded. Ventral side slightly 

 vaulted, in the immature individual almost flat. Coxal plates on the first free 

 thoracic segment produced forwards and acute. The 5th and 6th thoracic 

 segments are the longest ones. 



Abdomen a little longer than the last two thoracic segments together. 

 Last abdominal segment with the posterior margin rounded and about as long 

 as the 4th and 5th together. The first 3 abdominal segments with setae in their 

 lateral margins. 



