OPHIURANS OF THE PHILIPPINE AND ADJACENT WATERS. 121 



The first under arm plate is trapezoidal, a little longer than broad, 

 with a proximal border broader than the distal. The following plates 

 are rather small, pentagonal, with a very obtuse proximal angle 

 bounded by two straight sides, lateral borders slightly excavated by 

 the tentacle pores, and a rounded distal border notched in the middle ; 

 they are a little longer than broad. These plates are almost in contact 

 as far as the fourth ; be}^ond they are separated by an interval which 

 increases rapidly. 



The rather strongly projecting side arm plates carry at the base of 

 the arm five thick cylindrical spines, with the tip rounded, and pro- 

 vided with rather strong and very closely crowded denticulations 

 which are especially marked on the ventral spines. The first ventral 

 spine almost equals the segment in length, and the last dorsal does 

 not quite equal two segments. 



The single tentacle scale is rather small, short, and cylindrical, 

 with the tip obtuse, and its surface is covered with rugosities. 



The color of the specimen in alcohol is yellowish white. 



Affinities and distinctive features. — Ophioripa nugator is evidently 

 very close to the preceding species, from which it is immediately 

 distinguished by the large and thick spines on the dorsal surface of 

 the disk. It does not seem to me possible to suppose that O. margi- 

 nata may be an O. nugator in which these large spines have been 

 all torn away without leaving the least trace 1 of their insertion or 

 have not yet made their appearance. O. nugator also differs from 

 O. marginata in having the arms formed of shorter segments, in its 

 similarly shorter arm spines, in having the under arm plates more 

 elongated and almost in contact on the first segments, in the smaller 

 mouth papillae, and in having the tentacle scale also less developed. 



Genus OPHIOPHTHALMUS Matsumoto. 



The genus Ophiophthalmus was erected in 1917 by Matsumoto to 

 include a certain number of ophiurans assigned by authors to the 

 genera Ophiomitra or Ophiomitrella, or even to Ophiacantha. This 

 genus, very close to the genus Ophiomitrella, differs from it in having 

 the upper arm plates well developed and in contact on the first arm 

 segments, and in having the arm spines numerous and elongated, the 

 two rows on each side never coming close together in the median 

 dorsal line of the arm. In addition this genus shows on the dorsal 

 surface of the disk an investment of more or less imbricated plates, 

 which may be provided with rugose granules ; the naked radial shields 

 are rounded or oval. 



I agree perfectly with Matsumoto regarding the necessity of sepa- 

 rating the genera Ophiomitra and Ophiomitrella from forms such as 

 Ophiacantha normani Lyman, O. relicta Kcehler, Ophiomitra grani- 



