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The disk is tolerably large, and the arms gradually taper to 

 a point from the base, the terminal part being especially slender, 

 but not so conspicuous or long as in Perseplionaster misakiensis 

 (PL II, fig. 14, 15). 



Superomarginals. — The most conspicuous feature of this species 

 is the presence of three robust spines on the superomarginals, 

 forming a transverse series (PI. II, fig. 20). On a few plates in 

 the interbrachial arc there are usually only two of these spines 

 close to the inner edge of the plate, but there may also be four 

 or even five, in which case one of them is usually much smaller 

 than the others. In the terminal part of the arms there is usually 

 only one spine on each plate. Again the relative size of the three 

 spines is various, and any one of them may be the largest, although 

 this appoars to be most frequently the outermost one. The 

 central part of each superomarginal is covered with short conico- 

 squamiform spinelets, and these become subcapillary towards the 

 transverse grooves, which are well developed and the faces of 

 which are covered with capillary spinelets. The superomarginals 

 are nearly as high as broad in the greater part of the arms, and 

 their external face is perfectly rounded, so that the abactinal 

 and lateral faces can not be distinguished sharply. The two 

 marginals keep the same front on the outer side. 



Infer omar(jinals. — The inferomarginals are about as broad as 

 the superomarginals, and each plate carries three or sometimes 

 four robust spines ; the largest one close to the abactional end, and 

 the other two (or three) in a series with it on the actino-distal 

 face (PL II, fig. 19). When viewed from the side, the spines of 

 the two marginals make a single series, but those of the infero- 

 marginals are very apt to form a somewhat oblique row. Near 



