186 



THE OPHIURIDiE. 



the arm appears very high, but it is really rather low; its under side is flat. 

 On the tip of the side arm-plates there are three spines, the upper (outer) 

 one very short, the next somewhat longer, the lowest elongated and club- 

 shaped, enclosed in thick skin and with hooks at the end, which are also 

 hidden in the skin ; it is directed towards the under side of the arm, that is 

 to say upwards, because of the elongated side arm-plates. On the inner 

 part of the arm this spine lies flat on the under side, the side arm-plates 

 not being prolonged until farther out on the arm. This feature is seen in 

 all the arms. The two short spines are not transformed into hooks. The 

 arm-bones are distinctly seen through the naked skin. 



The radial shields are broad, covering almost the whole dorsal side of 

 the disk, not forming ribs, as in ^. Loveni and dispar. Finally the genital 

 slits are large, much longer than in the two named species, reaching 

 half way to the margin of the disk. 



Color in alcohol : gray. 



A young specimen of 5 mm. has the side arm-plates not yet very 

 elongated, but the genital slits are already very large. 



Stations 3424, 676 f., and 3426, 146 f. 



64. Asteronyx plana n. sp. 



Plate XXI. Figs. 3-4, Plate XXII. Pigs. 7-9. 



Diameter of disk, 10 mm. ; width of arms close to disk, 2 mm. ; length of 

 arms, 10-11 times the diameter of the disk 5 they are about equally long 

 and wide. Mouth papillae obscured by the skin, not conical 3 only one 

 conical papilla at the apex, and one row of teeth. (In young A. Loveni 

 there is also only one row of teeth, so that there cannot be any generic 

 value in this feature.) The side mouth shields are not elevated, there being 

 thus no elevated wall inside the genital slits; the whole under side is 

 quite flat. 



The arms are rather flat, not looking excavated, the side arm-plates not 

 being elongated. There are three well developed arm-spines, the two 

 upper (outer) ones as long as J-| of an arm-joint, the lowermost (inner) 

 as long as 1^^ joints, club-shaped, with roughened end, enclosed in skin, 

 but not so thickly as in the other Asteronyx species. The shorter spines 

 are not transformed into hooks. 



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