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104 



THE OPIIIURIDiE. 



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rated, almost oval, not half the length of the radius of the disk. In the 

 interbrachial spaces there are a median 



row of larger scales and some 



smaller ones on each side. Ventral side of the disk covered with scales 

 similar to those on the dorsal side. The edge of the disk rather sharp. 

 Genital scale indistinct, very narrow, reaching scarcely to the end of the 

 second joint. Genital slit short, reaching only to the end of the first joint. 



Two well developed arm spines, the upper one as long as or a Httle 

 longer than an arm-joint; farther out not quite so long as a joint; the 

 lower one a little shorter. The two inner arm-joints have no spines. One 

 lar^e, rounded tentacle scale on the outer side of the pore ; the first to 

 third pair of pores mostly have one or two indistinct scales at the 'inner 



si^'le (on the ventral plate). 

 Color in alcohol : white. 

 Several specimens from Stations 3362, 1175 fathoms; 3363, 978 f . j 



3366, 1067 f.; 3371, 770 f . ; 3400, 1322 f . ; 3413, 1360 f. 



Only unimportant variations to be noticed. The teeth sometimes are 

 serrate in outline, and the same may be the case with the infradcntal 

 mouth papilla. The mouth shield may be more rounded and a little longer. 

 The ventral plates in some specimens arc in contact till the 9th or 10th joint; 

 in younger ones they are so only on the first joints. The central plate some- 

 times is almost round ; the genital slits are often very indistinct, much 



shorter than first arm-joint. Sometimes, but rarely, there is an arm-spine 

 on the second joint, but then only on one side of the arm, and not on all 



arms of the specimen. 



This species is very closely related to 0. depressa Lym., but is not very 



The mouth shield, side mouth 

 shields, and ventral plates are of somewhat different shape, which will be 

 seen when comparing the figures of the two species ; the same is the case with 

 the disk scaling. The primary plates have a little central boss or tubercle 

 in 0, depressa; in 0. alba it is very indistinct, or not at all present. The 



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arm-spines are equally long, half as long as a joint in 0. depressa; in 0. alba 

 they are about as long as a joint on the inner part of the arm; farther out 

 shorter, only half the length of a joint. Usually the upper one is the 

 longest, but sometimes the lower one is so, sometimes they are equal. All 

 the pores have only one tentacle scale in 0. depressa ; the inner first to third 

 pairs of pores have two (three) tentacle scales in 0. alba. This character 

 seems to be of most importance ; however, it might well be that also in 



difficult to distinguish from the latter. 



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