154 



characters distinguishing them from one another being very slight and un- 

 important. 



Upon the whole the larval types 0. similis and formosus are among the 

 less interesting on account of their more generahzed features. But I have 

 thought it desirable to include them in this report in order not to exag- 

 gerate the impression that the Ophiurid larvae are easily arranged into 

 natural groups. That is the case with some forms, hke e. g. undulatus, costa- 

 lus; but the present forms are equally important as representing types 

 which do not lend any special support to a natural classification. 



Ophiopluteus fusus nova forma. 



Although there is only one specimen in hand, and that even in a very 

 far advanced stage of metamorphosis, as seen from the figure 83, A, 1 have 

 deemed it advisable to give a description of it, partly because the char- 

 acters to be seen on the remnants of the larva still attached to the young 

 Ophiurid are sufficiently marked for recognizing the species, partly because 

 it seems to show affinities to another Ophiurid-larva which stood hitherto 

 remarkably alone, viz. Ophiopluteus paradoxus. 



The main character of this larva is the peculiar thickening of the postero- 

 lateral rods a little above their basis. While the thickening increases very 

 gently from the base upwards, it ends rather abruptly outwards, the outer 

 part of the rod being very thin, with fairly long, thin, straight thorns on 

 either side (Fig. 83, C) ; the basal and thickened part is smooth. Also the 

 postoral rod has the same shape, although the thickening is less pronounced. 

 The other rods have already been absorbed, so that nothing can be said 

 about their structure. The body skeleton is simple, the end rods moderately 

 long, slightly bent in their outer parts. The transverse rods are irregularly 

 widened at the point; there is no median process. 



The shape of the posterolateral arms appears to be rather broad and 

 flat, as in 0. paradoxus. There is a distinct vibratile tuft at the posterior 

 end, as in the latter species. 



The single specimen in hand was taken at the Azores (38° 14' N., 24° 35' 

 W. 19/111. 1911. H. Blegvad). 



As stated above this species would appear to be nearly related to Ophio- 

 pluteus paradoxus, the larva of Ophiura albida Forb. They agree in the 

 characters of the body skeleton, the presence of a posterior vibratile tuft, 

 as in the general structure of the young Ophiurid, and probably also the 

 larval arms have the same shape in both; the only, essential difference is 

 the sweUing of the basal part of the posterolateral and postoral (a. o.?) 



