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THE OPHIURIDiE. 



153 



33. Amphiura assimilis n. sp 



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Plate X. Figs. 5-7. 



Diameter of disk^ 13 mm.; width of arm close to disk^ 2 mm.; length 

 of arms, c. 5-6 times the diameter of the disk. Two (in one specimen 

 three) small rounded, almost equally large mouth papilla) on each side, be- 

 sides those on the apex. The papilla of the first mouth tentacle is very 

 distinct, almost at the same level as the true mouth papillae. Mouth shield 

 equally wide and long, with the outer part restricted ; an obtuse angle 

 within, sides somewhat irregularly sigmoidly curved, corners rounded, 

 outer edge straight. Side mouth shields a little broader without than 

 within, where they meet. 



First ventral plate small, six-sided or rounded ; those beyond considerably 

 broader than long. They are rather broadly in contact, their inner end 

 thus being truncated ; farther out they are more or less distinctly separated 

 from each other, and have then an angle within. The outer edge, inner 

 and outer laterals, a little re-enteringly curved, outer corners rounded. Side 

 arm-plates, with spine-ridge not very prominent (though somewhat more 

 than shown in the figures). There is a little naked space between the side 

 arm-plates, not seen from the dorsal side. (Figure 5 is not correct in this 

 respect.) The dorsal plates are thrice as broad as long, with outer edge 

 slightly curved, a little concave on each side ; inner sides almost straight, 

 outer corners rather sharp; they are broadly in contact, the inner angle 

 very obtuse, tnmcatcd. The under side of the arms flat, the dorsal side 

 much x^oundcd. 



Disk covered with rather large, delicate, overlapping scales, among which 

 the primary plates are more or less distinct (scarcely at all in the specimen 

 figured). The radial shields pearseed-shaped, wholly separated by some few 

 rather large scales; they are pointed within, their outer edge rather broad, 

 straightly cut. Outside the radial shields are seen one or several narrow 

 scales. The scales of the under side smaller than those of the dorsal side; 

 usually there is one rather conspicuous scale joining the mouth shield. 

 Genital scales not distinct. Margin of the disk convex, the edge rounded. 



Three equal, short, thick arm-spines, scarcely longer than half the length 

 of an arm-joint. Two (seldom three) small tentacle scales, rather irregu- 

 larly arranged : that on the ventral plate is distinct only in the inner part of 



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