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180 



THE OPIIIURID^E 



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57. Ophiothamnus Isevis n. sp. 



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Plate XIX. Figs. 1-4. 



Diameter of clisk^ 4 mm. ; width of arm close to disk^ without spineS; 

 1 mm.; length of arms about five times the diameter of the disk. Four flat^ 

 pointed mouth papilla? on each side^ that on the apex a little larger; the 

 outer one of a somewhat different shape, having a cut on the inner side. 

 Perhaps it is not really a true mouth papilla. Mouth shield more broad 

 than long, with an obtuse angle within and a broad lobe without; corners 

 produced, sharp, inner sides slightly, outer deeply concave, outer edge 

 straight. Side mouth shields broader within than without, meeting witliin. 



First ventral plate rather large, five- or six-sided. Those beyond all 

 widely separated, with a very obtuse angle within and outer edge slightly 

 curved ; inner laterals straight or a little curved, outer re-enteringly curved, 

 outer corners produced, rather sharp. About twice as broad as long. Side 

 arm-plates with spine-ridge rather prominent. Dorsal plates triangular, 

 with outer edge curved, all widely separated, a little broader than long; the 

 first one quite rudimentary. Arms distinctly knotted. 



Disk almost wholly destitute of spines or grains, except on the scales in the 

 middle of the dorsal side, where are seen some few round grains, like those of 

 OpJdomitra granifera. ■ The radial shields are very large, as long as two thirds 

 of the radius of the disk; they are contiguous in most of their length, only 

 the inner ends being separated by a single large scale; they are almost 

 triangular, as broad as long ; the outer edge is slightly curved. In the 

 narrow interbrachial space there are some small scales, which in our speci- 

 men arc deeply sunk, so that there is a deep ridge; but that may be an 

 unnatural condition. The central part of the disk is covered with small 

 overlapping scales. On the under side of the disk there are a few large 

 plates; especially conspicuous are a usually symmetrical pair, which join the 



mouth shield. 



The first free arm-joint has five to six arm-spines, which form a continu- 

 ous series over the dorsal side ; the next joint has four, those beyond only 

 three ; the upper one is as long as 1|— 2 joints, the others about as long as a 

 joint; they are slender, feebly thorny. In the outer part of the arm the 

 lower spine is hook-like (Fig. 4). One rather large oval tentacle scale; 

 those on the first joint directed outwards. 



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