126 



to the young Ophiurid, being cast off when metamorphosis is completed. 

 (Comp. above, p. 124). 



The study of the numerous larvae of Ophiothrix (or of forms belonging 

 at least to the family Ophiothrichidae) which I have from different local- 

 ities: Japan, the Philippines, Malacca Strait, the Gulf of Aden, the Gulf 

 of Panama, California, the West Indies and the European Seas makes 

 evident the interesting fact, that it is simply impossible to find reliable 

 characters by which to distinguish with certainty the vari- 

 ous species of these larvae. There are some exceptions. The forms 

 described here as species c and d, especially the latter, are fairly well 

 characterized and easily distinguished ; but the forms designated as species 

 a and b certainly both comprise several species, as is evident from the 

 fact that they are found in widely separated localities (Europe, West 

 Indies, Panama, Japan), which have no species of Ophiothrichidae in com- 

 mon. If specimens of these larvae from the different localities were put 

 together, it would be impossible to separate the different species again. 

 Perhaps the pigmentation of the larvae may prove to be somewhat dif- 

 ferent, so that it would be possible to distinguish the species on having 

 the living specimens. But the pigmentation is liable to be more or less 

 destroyed on preservation. In the skeleton no reliable distinguishing cha- 

 racters can be pointed out. There may be some slight differences in the 

 length and thickness of the body rods and in I lie length of the median 

 processes; but I have been unable to find any definite specific characters 

 therein. In consequence of this fact I have thought it useless to give a 

 description of each of these larval species, which can only from zoogeo- 

 graphical facts be recognized as separate species. 



Species a. (PI. XIX, Fig. 1). The posterolateral arms are about three 

 times the length of the inner arms and generally have three large spots 

 of black pigment; some smaller pigment spots are found in the posterior 

 part of the body. The skeleton, see Fig. 53. 



To this type belongs the larva of Ophiothri.r Irayilis. Specimens not 

 distinguishable from this larva were found at Misaki, Japan (the species 

 represented in PI. XIX, Fig. 1); in the Malacca Strait (off Pulo Pisang, 

 1/XII, 1899); off the East end of Sokotra (XII, 1913); Taboga, Panama 

 (XII, 1915); San Diego, California (7/IX, 1915); St. Cruz, West Indies 

 (16/VI, 1915, H.Faye). Likewise the Ophiopluteus robustus (Echinodermen- 

 Larven d. Plankton-Expecl. p. 57. Taf. V. Fig. 3 4) from Fernando No- 

 ronha belongs to this type. 1 ) 



: ) In the place quoted I stated that this larva is undoubtedly nearly related to the Ophio- 

 //in'z-larva, then adding: "zu welcher Ophiure sie gehb'rt kann man nicht erkennen"; the 



