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172 



THE 0PHIURID7E. 



there is a spine at the outer angle. Side mouth shields broad, meeting 



within. 



First ventral plate rather large, with a truncated angle within, outer 

 edge almost straight. Those beyond very widely separated ; they have a 

 very small peak within, the inner laterals making almost a straight line 

 across the arm; outer laterals a httle concave, outer edge strongly curved, 

 outer corners rather sharp. They are very short, twice as broad as long, 

 only the second is a little longer than the rest. Side arm-plates very long, 

 with spine-ridge very prominent. Dorsal plates small, triangular, with outer 

 edge rounded ; almost equally broad and long, very widely separated. Arms 

 slender, very much knotted, the joints being deeply restricted at the inner 

 end, thick at the outer end, where ventral and dorsal plates are. 



Disk densely covered, above and below by very small grains or stumps, 

 about 0.1 mm. long, which end in a few spines (Fig. 8). The outer end of the 

 radial shields is uncovered, in mutual contact, their inner ends are rounded, 

 diverging; they do not make very prominent ridges. The outer end of the 

 radial shields directed somewhat upward, being thus a considerable distance 

 from the dorsal side of the arm. Perhaps this is an unnatural condition, but 



it is seen in all our specimens. 



Five-four slender smooth arm-spines, farther out only three. On the 

 second joint the two upper spines are as long as 3-4 arm-joints, the lower 

 only as long as one joint. Farther out they rapidly diminish in length, and 

 from the 7th or 8th joint also the upper spine is only about as long as one 

 arm-joint. One very small spine-like tentacle scale. 



Color in alcohol : gray. 



Several specimens from Stations 3417, 493 f; 3424, 676 I; and 



3425, 680 f. 



50^ Ophiacantha costata n. sp. 



Plate XVI. Fig. 10, Plate XVII. ligs. 4-6. 



Diameter of disk, 7 mm. ; width of arms close to disk, without spines, 

 1.5 mm.; length of arms about five times the diameter of the disk. Three- 

 five conical, finely thorny mouth papilla) to each side of mouth angle ; that 

 on the apex a little larger. Mouth shield almost twice as broad as long, 

 with an obtuse angle within and without, or with the whole outer edge 

 simply rounded ; side corners produced, inner (and outer) sides concave. 

 Side mouth shields broad, meeting within, a little curved. 



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