136 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



as broad. The following plates are large, and especially very broad, 

 almost twice as long as broad, pentagonal, with the proximal angle 

 very obtuse and formed by two short, slightly excavated sides; the 

 lateral borders are divergent and very strongly excavated by the ten- 

 tacle pores; the distal side is somewhat convex. These plates are 

 very widely separated by a space occupied by the side arm plates. 



These last are very strongly projecting in their distal part, which 

 forms a very marked rim on which are inserted the arm spines. 

 These number six or seven at the base of the arm. The length of 

 the four ventral spines increases very gradually from the first, which 

 is almost as long as the segment ; the three others on the dorsal side 

 are very much longer, and, at the base of the arms, the length of the 

 sixth and the seventh may reach five segments; sometimes the last 

 spine is a little shorter than that preceding. The four ventral spines 

 are provided with rather strong and closely set denticulations ; the 

 other spines are less strongly denticulated. 



The tentacle scale is single and of large size. It is especially large 

 on the first segment, where it is oval or rounded, and sometimes it is 

 doubled on the pores of the first pair; the size gradually diminishes 

 on the three or four following segments, and it then becomes lanceo- 

 late, while at the same time its borders become furnished with den- 

 ticulations, usually very marked, which cause it to be more or less 

 strongly spiniferous. In certain individuals it tapers more rapidly 

 than in others, but it is always much elongated. Sometimes, instead 

 of tapering in its distal half, it remains very broad, and even a little 

 broader than at the base ; this occurs, for example, in the specimen 

 from station 5219, shown in figure 6. 



Affinities and distinctive features. — Because of the occurrence of a 

 group of granules, replacing the last lateral mouth papilla and in- 

 serted on the adoral plate, as well as on account of the form of the 

 upper and under arm plates, Ophioplinthaca globata approaches O. 

 bythiaspis described by H. L. Clark ('11, p. 185), which was found 

 in Japan at a depth of 1,724 meters (943 fathoms). It differs from 

 it, however, in the form of the radial shields, which are broader and 

 closer together in each pair, and especially are not sunken; I have, 

 however, had occasion to note above that the radial shields of O. 

 globata are sometimes longer and narrower than usual (the individual 

 from station 5123, shown in figure 8). The arm spines are more 

 numerous, and the dorsal spines especially are much longer than in 

 O. bythiaspis; the mouth shields are broader than long, and the 

 under arm plates are more elongated; lastly, the tentacle scale is 

 also more developed, or at least so it seems to me. It is possible, 

 however, that the radial shields, much sunken in O. bythiaspis do 

 not constitute a specific character, as that feature, noted by H. L. 

 Clark, was seen only on a single specimen. But at present I do not 



