232 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



Among the species of Ophiothrix of the O. longipeda group a. 

 single one shows three light lines extending longitudinally over the 

 dorsal surface of the arms. This is 0. expedita which I described 

 from specimens discovered by the Siboga in the Sunda Archipelago, 

 and which has since been rediscovered at the Aru Islands ; this species 

 occurs also in the Albatross collection, as I have noted above. 



Apart from the general coloration, which differs in O. expedita and 

 O. rhabdota, the ornamentation of the arms is the same in the two' 

 species ; I am convinced that if the specimens studied by H. L. Clark 

 had been red instead of blue he would not have hesitated to apply to 

 them the name of O. expedita. Can a difference be found to separate 

 these two forms other than that shown by the coloration? I must 

 state first of all that 0. expedita shows in all its morphological char- 

 acters, as well as in its coloration, a remarkable constancy. The in- 

 dividuals collected by the Siboga at 10 different stations in the Sunda 

 Archipelago at depths varying between 13 and 73 meters, those which 

 I have recorded from the Aru Islands, and those collected by the 

 Albatross are quite identical and do not show the least trace of varia- 

 tion; it may be noted, furthermore, that the general red coloration 

 is sometimes rather bright,- and sometimes darker and verging toward 

 brown ; this may depend on the preservation, and also on the age of 

 the individuals. I note also that the two dark lines which extend on 

 either side of the median longitudinal white line of the arms are 

 sometimes perfectly continuous, and sometimes interrupted, and that 

 their borders are sometimes straight and sometimes slightly sinuous ; 

 these details are of no importance. I have compared with the great- 

 est care the different specimens of 0. expedita which I possess with 

 two specimens of 0. rhabdota collected by the Albatross, and I must 

 say that, apart from the coloration, it has been impossible for me to 

 recognize between them the slightest difference in structure. The blue 

 coloration of O. rhabdota does not appear to be absolutely constant; 

 of the two specimens at hand, one shows a rather dark-blue general 

 coloration, mixed only with white, while in the other this blue colora- 

 tion, which is a little paler, is grayish and mixed with red, the color of 

 typical 0. expedita. Under these conditions I would be rather in- 

 clined to consider H. L. Clark's 0. rhabdota as a blue variety of O. 

 expedita. 



The conspicuously red coloration of 0. expedita sharply separates 

 typical examples from related forms of the 0. longipeda group, 

 especially from O. longipeda (Lamarck) and from 0. puncto-limbata 

 Martens, but as there occurs in O. expedita a blue or gray blue variety 

 which corresponds to the form rhabdota it is worth while to recon- 

 sider the distinctive characters of these two species and of 0. expe- 

 dita. This last is evidently very close to 0. longipeda, which it re- 

 calls in the arrangement and the characters of the arm spines, as- 



