OPHIURANS OF THE PHILIPPINE AND ADJACENT WATERS. 431 



border becomes rapidly smaller, and gives place to an acute angle; 

 the plates then become pentagonal. At some distance from the disk 

 they assume a simply triangular form and are separated by a narrow 

 interval. 



The side arm plates, which project only slightly, bear three very 

 slender cylindrical and pointed arm spines, which are usually 

 appressed against the lateral surface of the arms; their length does 

 not reach usually half the length of the segment. The two or three 

 first arm segments often bear four spines ; the two dorsal spines are 

 usually close to each other, while the ventral spine is somewhat sepa- 

 rated from the little group thus formed ; but this arrangement is only 

 noticeable on the first arm segments. 



The rather large tentacle pores are provided with two scales 

 throughout the length of the arms ; these scales are subequal and of 

 medium size. 



The color of the specimens in alcohol is white or slightly yellowish. 



Affinities and distinctive features. — OpMozonella subtilis is evi- 

 dently very close to O. molesta, which it recalls by the form of the 

 mouth shields ; it is distinguished from it by its very much less robust 

 habitus, by having the arms narrower, relatively longer, and tapering 

 less rapidly. The plates of the dorsal surface of the disk are very 

 numerous, rounded, and separated by other extremely small plates; 

 the radial shields are more elongated. The adoral plates are thicker 

 and shorter; the oral plates are larger. The upper arm plates are 

 triangular from the third or the fourth outward, and the two tentacle 

 scales are appreciably smaller in 0. subtilis than in O. molesta; the 

 arm spines also are slender, ordinarily shorter and smaller, appressed 

 against the side arm plate, and not very evident ; they are sometimes 

 four in number on the first arm segments and the first ventral spine 

 is separated from the others, a feature not found in O. molesta. 



These differences certainly are not due to the age of the individuals, 

 or to their lesser size. The comparison with small specimens of O. 

 molesta, such as those from station 5429 and the small one from sta- 

 tion 5114, of which I give photographs here and of which I described 

 the characters above, is quite conclusive and shows well that the two 

 species are very distinct. 



OPHIOZONOIDA OBSCURA, new species. 



Plate 80, figs. 8, 9, 13. 



Locality. — Albatross station 5255 ; Gulf of Davao ; Dumalag Island 

 (S.) bearing S. 65° W., 8.34 kilometers (4.5 miles) distant (lat. 7° 

 03' 00" K, long. 125° 39' 00" E.) ; 183 meters (100 fathoms) ; May 

 18, 1908 ; sft. M. 



A single specimen (Cat. No. 41155, U.S.N.M.). 



