452 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



abactinal integument between the fascicles of spinelets is thrown 

 into numerous irregular wrinkles. 



On the midradial region the abactinal plates have usually 3 trun- 

 cate lobes and on the lateral region 4, by which they overlap strongly, 

 the small meshes containing 1, 2, or rarely 3, papulae. 



The marginal plates are conspicuous, low, transverse ridges 

 oriented obliquely and bent aborad, so that each pair of marginals 

 appears to form a chevron, the angle of which is toward base of ray, 

 for the reason that the lower end of each superomarginal touches the 

 upper end of the corresponding inferomarginal. A long series of 

 chevrons thus occupies the side of each ray. Superomarginals 40. 

 The spine-bearing crest has the appearance of being bent aborad and 

 the upper end is in the form of a slight knob which bears 3 promi- 

 nent, tapering, sharp, closely appressed spines (the median usually the 

 longer), which, relative to the width of plate, are more prominent 

 distally ; 6 to 9 much slenderer, shorter spinelets continue this series 

 to the lower end of the plate, and at the same time become shorter; 

 these spines are united by a web. 



The inferomarginal plates are formed and armed just like the 

 superomarginals, except that the long spines (3 or 4 in number) are 

 at the lower or actinal end and are longer than the corresponding 

 superomarginal spines, being slightly longer than the extreme width 

 of plate. Three to 5 small spines continue this series toward the 

 intermarginal line. The large inferomarginal spines are on the 

 angle between the lateral and actinal faces of the ray, and proxi- 

 mally a fourth spine is added to the actinal end of the series. The 

 points of the spines frequently converge (the median being longest) 

 and the group has then the appearance of Sladen's figure of the 

 " actinal intermediate " spines of R. vannipes. The inferomarginal 

 series of X. polyctenius evidently corresponds to the series of plates 

 described by Sladen as actinal intermediates. When the marginals 

 are cleaned they are seen to be imbricated in their own series, the 

 adoral end slightly overlapping the aboral end of the next plate 

 toward the mouth. The plates are curiously formed and slightly bent, 

 the outer end of each suggesting the end of a femur flattened or the 

 dorsal end of a rib. The intermarginal end is narrower as if the bone 

 had been cut off at that point. 



Actinal intermediate plates about 3 only, just back of the mouth 

 plates, and bearing a very few spinelets. 



Furrow spines 9 or 10, distally 8, united by membrane for two- 

 thirds their length into a prominent scoop-shaped fan very much as 

 in R. vannipes. The central 3 or 4 are longest, and are equal in length 

 to about 1^ the base line of the comb. On the surface of the plate is 

 an oblique comb of 4 stouter, tapering, sharp spines, the 2 median 

 the longest and slightly longer than the furrow spines. The sub- 



