OPHIURANS OF THE PHILIPPINE AND ADJACENT WATERS. 79 



long. 127° 15' 00" E.) ; 763 meters (417 fathoms) ; November 27, 

 1909; gy. M. 



Five specimens. 



Albatross station 5648; Buton Strait; North Island (S.) bearing 

 N. 87° E., 18.90 kilometers (10.2) miles) distant (lat. 5° 35' 00" S., 

 long. 122° 20' 00" E.) ; 1,022 meters (559 fathoms) ; December 16, 

 1909 ; gn. M. 



One specimen (Cat. No. E.181, U.S.N.M.). 



Notes. — On account of the arrangement of the mouth papillae this 

 species appears to me to find its place rather in the subgenus Ophio- 

 treta Verrill than in the group Ophiectodia, to which I had at first 

 assigned it. 



The numerous series of specimens collected by the Albatross show 

 that O. matura is subject to very considerable variation, and exhibit 

 characters which at first sight seem to separate them widely from 

 the type which I described on the basis of two specimens collected by 

 the Siboga in latitude 5° S. and longitude 132° E., in 797 meters 

 (435 fathoms) of water. The variations especially affect the arma- 

 ture of the disk and of the upper arm plates, the form of the tentacle 

 scale, the form of the mouth shields, and the transformation of the 

 first ventral arm spine into a hook. 



In the two Siboga specimens the dorsal surface of the disk was 

 covered with small narrow and slender club-spines terminating in 

 two or three unequal and irregular spinules. This condition is 

 rather rare in the Albatross series ; I notice it in the specimen from 

 station 5492, and in one of the two from station 5359 (pi. 12, fig. 6), 

 in which these club-spines are rather unequal, not close together, and 

 very short in the central region of the disk, becoming more or less 

 elongated toward the periphery. In the specimen from station 5467 

 the club-spines are more elongated and almost of equal length, 

 though they are still rather short; but in the majority of the others 

 they have become very long, closely crowded, and always very slender 

 true spines; sometimes these spines are smooth throughout and re- 

 main of the same diameter to the extremity which is ordinarily 

 bifurcated, or terminated by three or four small spinules (pi. 12, 

 fig. 1; pi. 14, figs. 1, 4; pi. 15, fig. 2) ; sometimes they are somewhat 

 conical, showing denticulations over a greater or lesser portion of 

 their length (pi. 13, fig. 2; pi. 15, fig. 1). On this point there is 

 the greatest possible variation, of which the numerous photographs 

 which I reproduce (pi. 95, figs. 2a and b) will give an idea. 



The upper arm plates as a rule have their distal border armed with 

 small spines which are more or less numerous and more or less devel- 

 oped. Sometimes they are reduced to small short and conical spine- 

 lets as I described them in the types; this is the condition seen, for 



