328 A HISTORY OF RECENT CRUSTACEA 



Neotanais) loivisjnnosus and Strongylura arctophylax, 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, 

 Strongiiltira cylindrata, Sars. The Australian species, 

 Paratanais linearis, Haswell, should perhaps be transferred 

 to Anarthrura, hitherto represented only by Auarthrura 

 simplex, Sars, from Norway. 



There are difficulties connected with the study of the 

 Tanaidae, 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 an inch. 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 Tanaidas 

 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, i^. which 

 the Tanaidge have no share, while the Tanaidee, on their 

 side, have characters of the mouth-organs foreign to all 

 the Amphipoda. The form and position of the heart, 

 extending in the Tanaida? from the first to the last segment 

 of the perfeon, very nearly as in the Amphipod GoroiDliium^ 

 and the other resemblances in the circulatory apparatus of 

 the two groups, pointed out by M. Yves Delage, afford the 



