84 



radial shield, a row of roundish scales ; interbrachial spaces below 

 covered with very short spines. Radial shields smaller than usual ; 

 regular triangular, quite naked; length to breadth, 2.8 : 1.6. Arm- 

 spines, near base of arm, from five to seven ; the two or three lowest 

 very small ; the larger ones swelled at the tip ; lengths to that of 

 under arm-plate, 2.2, 2.5, 2.2, 1.1, .6 : .6. Tentacle-scale very small, 

 somewhat pointed. Color, in alcohol, above, disc bright Prussian 

 blue, varied with whitish ; outer tips of radial shields white ; arms 

 obscurely banded with paler and darker blue ; a longitudinal stripe 

 of dark-blue along the middle, and a small white spot between each 

 pair of upper arm-plates ; below, interbrachial spaces dark-blue ; 

 mouth parts and under arm-plates nearly white. 



Variations. Another specimen had the disc of a more intense 

 blue, and the white spots on the arms were nearly wanting. 



This species approaches 0. nereidina^ but has more rows of scales 

 on the back of the disc ; the arms, also, are proportionately shorter. 

 Kingsmill Islands. 



Ophiothrix Cheneyi, LjTiian. 



Special marks. Radial shields closely granulated ; disc beset with 

 thorny stumps. Length of arms about eight times the diameter of 

 disc. 



Description of a specimen. Diameter of disc 21 millim. Width of 

 arm, without spines, 3.6 millim. Length of arm, 1 70 millim. Tooth- 

 papillae very close set ; they form, as usual, a vertical oval, bordered 

 by a projecting margin of about twenty-six papillre, the centre being 

 filled in with smaller and lower papillse. Teeth, two. Mouth-shields 

 nearly as long as broad, heart-shaped with a pretty acute point in- 

 ward ; length to breadth, 2.3 : 2.5. Side mouth-shields somewhat 

 variable, more or less closely soldered to the mouth-shields. Under 

 arm-plates partly separated by transverse furrows ; rectangular, 

 broader than long, re-enteringly curved outside ; length to breadth 

 (10th plate), 1 : 1.3. Upper arm-plates much broader than long, 

 oval, well-marked, with a distinct longitudinal rib, sometimes a dent 

 in the outer side; length to breadth (12th plate), 1.1 : 2.8. Disc 

 above, closely beset with little stumps, thorny on their tops and sides ; 

 the longest of them 5 millim. long. Below, interbrachial spaces with 

 scattered stumps, which near the mouth-shields are more pointed and 

 fewer. Radial shields indistinct, from being covered with large, 

 rough grains, about 35 to a square millim. Arm-spines 9 ; the 3d, 

 4th, and 5th, longest, pretty stout, somewhat thickened at the point ; 

 the three under ones very small, as also the upper one, which is not 

 always found ; lengths to that of under arm-plate, .5, 2.9, 3, 3.1, 3.1, 

 2, 1.5, 1.2, .5 : 1.2. Tentacle-scales, oval ; small but distinct. Color, 

 in alcohol, above, disc rich Prussian blue, speckled with white ; a 



