328 A HISTORY OF RECENT CRUSTACEA 
Neotanais) levispinosus and Strongylura arctophijlaw, all 
of Norman and Stebbing, taken off the coast of Ireland, 
may be regarded as British. The last, however, is not 
very markedly distinct from the Norwegian species, 
Strongylura cylindrata, Sars. The Australian species, 
Paratanais linearis, Haswell, should perhaps be transferred 
to Anarthrura, hitherto represented only by Anarthrura 
simplex, Sars, from Norway. 
There are difficulties connected with the study of the 
Tanaidee, owing to the differences that often exist between 
the two sexes, to the likenesses that sometimes exist be- 
tween the females of different species, and to the prevailing 
minuteness of size, which descends even to one-twentieth 
of aninch. That many of the genera are blind is readily 
to be explained in connection with their habit of living 
ensconced in the sand. When their little white or 
pellucid bodies are discerned amidst the fragments of 
crystal, shells, polyzoa, foraminifera, and spines of urchins, 
it is seen that these components of the sand often exceed the 
Tanaids in size. It is not unlikely, therefore, that many of 
the species have been frequently overlooked, and that in the 
future those already known will be discovered in many 
fresh localities, and that many fresh species will eventually 
be brought to light. 
There is a still pending dispute whether the Tanaidze 
should maintain their position among the Isopoda or be 
transferred to the Amphipoda, or be separated from both 
and raised to the dignity of an independent sub-order. Of 
these plans the least advisable seems to be that which 
would mix them up with the Amphipoda, for that enormous 
group is at present separated from all other Crustacea by 
characters of the branchial organs and the pleon, in which 
the Tanaide have no share, while the Tanaidz, on their 
side, have characters of the mouth-organs foreign to all 
the Amphipoda. The form and position of the heart, 
extending in the Tanaide from the first to the last segment 
of the perzeon, very nearly as in the Amphipod Corophium, 
and the other resemblances in the circulatory apparatus of 
the two groups, pointed out by M. Yves Delage, afford the 
—— tc J 
