OPHIURANS OF THE PHILIPPINE AND ADJACENT WATERS. 245 



preceding individual. The two specimens from station 5187 possess 

 only spines, but these remain rather short, slender, and well spaced 

 (fig. 5). In a specimen which was sent to me by the United States 

 National Museum and which was determined by H. L. Clark (station 

 4833, Shima Hondo, 79 fathoms) the spines are remarkably devel- 

 oped; they are stout, thick, and elongated especially in the central 

 region of the disk, becoming shorter toward the periphery. Another 

 specimen, which was also sent to me by the National Museum, and 

 which came from station 4893, is remarkable for the feeble develop- 

 ment of the armature of the dorsal surface of the disk ; as is shown 

 by the photograph which I give of it (fig. 6), the outlines of the 

 dorsal plates of the disk, which are relatively large, and each of 

 which only bears a very small club spine, are easily distinguishable. 

 In the specimen from station 5187. which I have already mentioned^ 

 the armature of the disk also is rather slightly developed ; the plates 

 are separated from each other by soft parts, especially in the central 

 region where they are never in contact. 



I include (pi. 99, figs. 4#, &, and c) some photographs of club spines 

 and of isolated true spines which will show the principal forms found 

 in O. koreana. The trifid or sometimes quadrifid club spines shown 

 at a represent the normal form, which is most frequently observed 

 when the disk bears nothing but club spines. When true spines occur 

 among the club spines, and before these become transformed into 

 small true spines, abnormal forms are sometimes found, such as 

 those which are shown in fig. 45 / the three spinules instead of becom- 

 ing long and subequal are very much shortened; they become very 

 unequal, and their number falls to two, or they may even disappear 

 altogether, so that the club spine is reduced to a very elongated cone. 

 I show at c different forms of spines, some very short, others much 

 developed, as I observe them, for example, in the specimen from 

 station 5179, the whole dorsal surface of which is shown on plate 45 

 as figure 1. 



In all the specimens in the collection which has been sent me the 

 radial shields are very large, whether they are completely naked or 

 covered with a greater or lesser number of club spines, and I con- 

 sider that this relatively large size of the radial shields constitutes 

 one of the specific characters of O. koreana; it may already be 

 noticed in the smallest specimens. The shape of the upper arm plates 

 is also very characteristic, and I find it the same on all the adult 

 specimens. The photographs which I include (pi. 45, figs. 1, 2, 4, 5, 6) 

 give a good idea of the outlines of these plates; the distal angle 

 makes a sort of rounded and slightly projecting beak, and the two 

 sides which bound it are very slightly turned inwardly instead of 

 being straight, or even somewhat convex, as is the case in the species 

 of Ophiotlirix related to O. koreana. 



