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as an established fact through the "Brachiolaria hibernica'' of Gemmill, 

 affords another important aid for settling the question of the parentage of 

 the larva. Asterias tenuispina does not occur in the Atlantic to the North 

 of 40° Lat. N. Accordingly its larva could hardly be found off Ireland. 

 On the other hand Pedicellaster sexradiatus is not known to occur farther 

 North than the Biscayan Gulf; but it is by no means improbable that it 

 does, however, occur in the deep-sea off Ireland. The result is then that 

 it seems highly probable that the " Stellosphsera mirabilis" is the larva of 

 Pedicellaster sexradiatus. 



The Ophiopluteus, in spite of the great number of "species" known, 

 appears to show only unimportant deviations from the original simple 

 type, which may perhaps be most nearly represented by the Ophiothrix- 

 larva. In the shape of the body there are only few features which may be 

 regarded as a higher specialization ; such feature is the presence of vibratile 

 lobes at the base of the posterolateral arms in the Ophiocoma-\ar\a. The 

 presence of a ciliated tuft at the posterior end of the body, occurring in 

 various forms, may also be a specialized feature, probably acquired separ- 

 ately in various groups. But too little is known for forming a definite judg- 

 ment of the value of this character. The ciliated ring in the posterior end of 

 the body of Ophiopluteus coronatus ("Echinodermen-Larven d. Plankton- 

 Exped." Taf. VI, Fig. 6), as yet quite a unique feature in Ophiurid-larvse, 

 may perhaps represent a further specialization of the apical tuft. But so 

 long as we do not know anything about the affinities of that larva ( — its 

 skeletal structure is still unknown — ) this question must remain unsettled. 



The length of the arms varies very considerably. The posterolateral arms 

 are generally much the longer and form the main floating apparatus of 

 the larva;, this is especially evident in the OphiothrixAsiwa and Ophiopl. 

 opulentus, where these arms are entirely unaltered during metamorphosis, 

 the young Ophiurid remaining attached to them and simply leaving them 

 by the time it is giving up pelagic life. The arms of Ophiurid-larvse never 

 become actively movable swimming organs, no muscles connecting the 

 two parts of the body skeleton being present, contrary to what is often 

 the case in Echinoid larvae. Generally the arms are very thin and narrow, 

 more rarely broad and flat (as in Ophiopl. paradoxus and the Ophiocoma- 

 larva). The widening of the arm points often found in preserved speci- 

 mens is probably only due to preservation. It is a curious fact that the 

 right anterolateral arm is often longer than the left one. 



A very conspicuous feature is the absence of posterodorsal arms in the 

 larva of Amphiura filiformis (Ophiopluteus mancus). Also in Ophiopluteus 

 dubius (Echinodermen-Larven d. Plankton-Exped. Taf. IV. Fig. 9—10) the 



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