OPHIURANS OF THE PHILIPPINE AND ADJACENT WATERS. 357 



Ophiomastus because of the development of the tentacle pores and 

 the large size of the mouth shields which cover the whole ventral 

 surface of the disk; but the rudimentary state of the radial comb 

 and the low form of the disk separate it from the majority of the 

 species of the former genus. But the radial papillae, slightly devel- 

 oped though they are, nevertheless occur, and the same low form of 

 the disk is found in O. depressus which the Siboga dredged in 4° S. 

 latitude and 118° E. longitude in 2,029 meters (1,110 fathoms). The 

 new species is distinguished from the latter by having the plates of 

 the dorsal surface of the disk reduced to the primary rosette, and 

 by having only two arm spines. 



AMPHIOPHIURA CANALICULATA, new species. 



Plate 82, figs. 10-12. 



Locality. — Albatross station 5356; North Balabac Strait; Balabac 

 Light bearing S. 64° W., 28.72 kilometers (15.5 miles) distant (lat. 

 8° 06' 40" N., long. 117° 18' 45" E.) ; 106 meters (58 fathoms) ; 

 January 5, 1909 ; S., Sh. 



One specimen (Cat. No. 41341, U.S.N.M.). 



Description. — The specimen is almost entire, one of the arms only 

 being broken off near the base. The diameter of the disk is 8 mm. ; 

 the arms are 16 mm. long. 



The disk is rather thick, with the two surfaces slightly convex; 

 the arms are rather slender, almost as high as broad, and they taper 

 rather slowly to the tip, which is pointed. 



The dorsal surface of the disk is covered with rather large plates 

 which are few in number. The central rosette covers almost half 

 the width of that surface; the dorso-central plate is large and pen- 

 tagonal; the five primary radials have almost the same dimensions, 

 but they are somewhat unequal; they are broadened transversely 

 and their distal border is strongly convex. Following each one of 

 them there is in the radial space a single very much smaller and 

 especially shorter plate which is trapezoidal with the distal border 

 broadened and strongly convex, and which separates the two radial 

 shields of each pair in their proximal region. The interradial spaces 

 are each occupied by a series of three plates, the first very large and 

 the second smaller; the third, which is very much broader, occupies 

 the periphery of the disk and even passes over onto the ventral sur- 

 face. On either side of the last three are to be seen two very much 

 smaller plates situated outside the radial shield and also on the 

 periphery of the disk. The radial shields are markedly smaller than 

 the six primary plates; they are irregularly quadrangular, twice as 

 long as broad, strongly divergent, and in contact for about a third 

 of their length. The radial papillae are large, elongated, cylindrical, 

 and tapering to the slightly rounded extremity. 



