210 s. goto: 



On each superomarginal plate (PI. II, fig. 23, 28) can be dis- 

 tincuised a central transverse area of coarser armature. This is 

 most conspicuous in the middle portion of the arm, but is less so 

 on the first few plates, as well as on the plates belonging to the 

 distal slender portion. Moreover, in the greater part of the arm 

 there are in this area 3-5 conspicuous, pointed, somewhat flattened, 

 subconical spines, forming a transverse series. These conspicuous 

 spines are of unequal sizes even on the same plate, and are mostly 

 present on the outer rather than on the inner portion. The 

 remaining surface of the superomarginal is uniformly covered with 

 very fine silky subcapillary spinelets, which gradually pass into 

 the truly capillary spinelets clothing the surfaces of the trans- 

 verse grooves, which are less deep and more open than in Astro- 

 IJecten. In the interradial angle the superomarginals stand out 

 very slightly more than the inferomarginals, but in the larger part 

 of the arms the latter are more projecting, so that the lateral 

 margin is formed entirely by them. 



Inferomarginals. — The inferomarginals (PL II, fig. 24, 26) are 

 very broad in the greater part of the arm, but less so in the 

 interradial angle and the distal slender portion. The first infero- 

 marginal is very slightly higher than broad, the second and tliird 

 are a httle broader, while the next following seven or eight are 

 of nearly equal breadth, the remaining plates gradually decreasing 

 in breadth towards the slender portion of the arm, where they 

 undergo aorain a sudden decrease in breadth. The general 

 armature of the actinal sm^face of the inferomarginals may be 

 described as scaly, the scales being of unequal lengths, directed 

 obliquely outwards and distally, and overlapping one another. 

 Towards the inner margin of the plates the scales are more or 



