OPHIURANS OF THE PHILIPPINE AND ADJACENT WATERS. 81 



I notice that the first ventral arm spine may be transformed into 

 a hook at a greater or lesser distance from the base of the arms, and 

 in the distal part of the arm this transformation always takes place 

 (pi. 15, fig. 3) ; but sometimes, as is seen, for instance, in a speci- 

 men from station 5424, shown on plate 14, figure 2, this transforma- 

 tion appears very early and already shows itself on the tenth arm 

 segment. It may happen also that the second spine has the ex- 

 tremity recurved and that its teeth become very large, though rather 

 few, on its proximal or concave border, and that it, too, thus tends 

 to become converted into a hook. On plate 95, figure 2, I give some 

 photographs showing the forms which the first (d) and the second 

 (c) ventral arm spines may assume. 



I may add that the arm spines, which are more or less elongated, 

 are sometimes very long and extremely slender, and almost silky, 

 as for example in the specimens from station 5424 (pi. 12, fig. 1, and 

 pi. 14, fig^ 1) ; they are still longer but thicker in that from station 

 5526 (pi. 13, fig. 2), but very much shorter in that from station 

 5359 (pi. 12, fig. 6). 



All of these variations do not' prevent the recognition of the 

 species when there are at hand specimens enough to follow the vari- 

 ous phases, but with a single specimen one might very easily be 

 led into error. It is for this reason that it has seemed to me ad- 

 visable to describe these variations in some detail, and especially 

 to include a number of photographs showing the most characteristic 

 forms of O. matura. 



The transformation of the first ventral arm spine into a hook at 

 some distance from the base of the arms is a very remarkable char- 

 acter, though I do not believe it should be considered of sufficient 

 importance to necessitate a generic separation, and I therefore leave 

 O. ma.tura in the genus Ophiotreta near O. gratiosa, to which it is 

 very closely related. I have not been able to observe the least in- 

 dication of a transformation into a hook of the first ventral arm 

 spine either in O. gratiosa or in the other species of Ophiacanthidae 

 of which the arms are preserved throughout their entire length. 



OPHIOTRETA SPATULIFERA, new species. 



Plate 19, figs. 5, 6. 



Locality. Albatross station 5629; Patiente Strait and southward; 

 Doworra Island (S.) bearing S. 62 W., 11.1 kilometers (6 miles) 

 distant (lat. 50' 00" S., long. 128 12' 00" E.) ; 375 meters (205 

 fathoms) ; December 2, 1909 ; co. S. 



One specimen (Cat. No. 41197, U.S.N.M.). 



Description. The diameter of the disk is 8.5 mm.; the arms are 

 broken off near the base, but the greater part of the fragments are 



55269 22 Bui. 100 6 



