588 THE AMERICAN NATURALIST.  [Vou. XXXII. 
H. Ludwig,! treating of the distribution of the holothurioids, 
crinoids, and ophiuroids, with special reference to their polar 
ranges. The part on the holothurians is especially interesting, 
since it was this group that first suggested to Théel the idea of 
bipolarity. According to Ludwig there are no bipolar species, 
and, in respect to the genera, there is not a single instance that 
shows the slightest indications of bipolarity. Out of 10 genera 
found in both polar regions, 5 (Stichopus, Cucumaria, Thyone, 
Phyllophorus, Chirodota) have been found abundantly in the 
littoral parts of the tropics, and 4 (Bathyplotes, Mesothuria, 
Trochostoma, Ankyroderma) are connected in the deep sea; 
and the same seems to be true of Psolus, which has been 
reported from tropical latitudes, although it seems to be rarer 
there. Aside from these 10 genera mentioned, there are 9 
genera peculiar to the Antarctic, and 6 peculiar to the Arctic 
(but some of them extend into the tropics), thus giving a 
different character to the two faunas. The general result in 
the other two groups studied by Ludwig is practically the same; 
there are no bipolar species, and the number of genera peculiar 
to each fauna is larger than the number of genera common to 
both. Among the crinoids there is only 1 genus (Antedon) 
found in both areas, while 3 are peculiar to the Antarctic (2 of 
them abyssal) and 1 peculiar to the Arctic, and among the 
ophiuroids 6 genera are common to both areas, while 9 are 
peculiar to the Antarctic and 8 to the Arctic. 
The genus Antedon found in both polar seas is very interest- 
ing. Both the Antarctic and Arctic species belong exclusively 
to two sections of the genus, A. eschrichti and A. tenella. The 
Tenella group is found in all parts of the world, so that there is 
nothing remarkable about its distribution. The Eschrichti group, 
however, contains 4 littoral Antarctic species and 3 littoral Arctic 
species (2 of them also abyssal), the latter all from the North 
Atlantic. Now it is very significant that some kind of a con- 
nection is afforded by one of the Antarctic species, namely, 
A. rhomboidea. This species has been found in the littoral of 
the southern end of America, and its range extends northward 
1 Hamburger Magathaensische Sammelreise. WHolothurien, 1898; Crinoideen, 
1899; Ophiuroideen, 1899 
