148 BULLETIN OF THE 



den. Seven long, slender, translucent arm-spines, essentially smooth, only tlie 

 lower ones being slightly rough under the microscope. Lengths to that of an 

 arm-joint 3.5, 3.5, 3.5, 2.8, 1.8, 1.3, .8 : .8. Tentacle-scales narrow and sharp. 

 Color in alcohol, white. 



The great size of the side arm-plates and the number and length of the arm- 

 spines mark this as an immature specimen, but the specific characters are not 

 found in any other. 



Station 214, 500 fathoms, 1 specimen. 



Ophiacantha serrata sp. nov. 



Plate X. Figs. 273, 273. 



Special Marks. — Disk closely and evenly set with minute grain-like stumps 

 bearing a crown of blunt thorns ; arm-spines long, slender, strongly thorny, 

 translucent, mounted on steep, narrow, much projecting side arm-plates. 



Description of an Individual (Station 219). — Diameter of disk 6 mm. Length 

 of arm about 32 mm. Width of arm without spines 1.8 mm. Seven flat, 

 rather blunt mouth-papillse, not crowded ; the innermost one much larger and 

 squarish ; besides these, the first under arm-plate bears two tentacle-scales, one 

 to each of second pair of mouth-tentacles. Four flat teeth, similar in shape 

 to the innermost mouth-papilla. Mouth-shields much wider than long, of a 

 transverse diamond-shape, Avith lobe-like angles. Side mouth-shields straight 

 and narrow, nearly or quite meeting within. First under arm-plate small and 

 rounded, and bearing on its inner edge two tentacle-scales ; second plate long 

 axe-shaped, A\dth a curve without, a well-marked angle within, and lateral 

 sides re-enteringly curved ; third plate proportionately shorter and with the 

 inner side a very obtuse angle. Upper arm-plates small, of a wide fan-shape, 

 with the angle inward. Side arm-plates large, meeting widely above and be- 

 low, rising very suddenly to form a high, narrow spine-ridge, so that the arm 

 has the look of a series of short cylinders alternating with burrs (Fig. 272). Disk 

 densely and evenly beset with minute grain-like stumps, bearing a crown of 

 blunt thorns (Fig. 273). Scaling and radial shields covered, except outer tips 

 of the latter. Nine long, slender, translucent, strongly thorny arm-spines ; 

 lengths to that of an arm-joint 4, 4, 4, 3.2, 2.7, 2.5, 1.8, 1.8, 1.3 : 1. One small 

 spiniform tentacle-scale. Color in alcohol, white mottled with pale brown. 



The small number of teeth and large side arm-plates show the specimen to 

 be youn<,', but the specific marks are good, and would be carried forward to the 

 adult, which doubtless has ten or a dozen long, -lassy, thorny arm-spines, with 

 side arm-plates not so exaggerated in their projection. 



Station 219, 152 fathoms, 1 specimen. 



