212 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



Superomarginal plates confined to side wall of ray, and much 

 longer than high. Each bears a long, slender, tapering spine, close 

 to the upper margin, 8 or 9 mm. long (equal to about 1^ plates in 

 length). The first 4 plates have usually 2 unequal, accessory spines, 

 together with 3 or 4 slender spinelets. Beyond this point there is at 

 first 1 accessory spine, much shorter than the principal spine, and 

 gradually this decreases in size and merges in with the 2 or 3 spine- 

 lets which accompany the principal spine. The interradial plate is 

 higher than the rest and bears at the upper end 4 prominent spines, 

 one of which is generally larger than the rest. 



Inferomarginals very nearly opposite superomarginals, not alter- 

 nate as Alcock states is the case with violaceus. Inferomarginal 

 spines 2, the lower the shorter. Very conspicuous pedicellariae with 

 2 semicircular or arcuate combs (containing upward of 10 spines) 

 are present on the transverse suture between nearly all the infero- 

 marginal plates except the last dozen. The general surface of the 

 marginal plates is bare except for a few widely scattered spinelets. 



Actinal intermediate areas small, with 8 to 12 large pedicellariae. 

 The plates bear 1 to 3 slender spinules. 



Furrow spines 8 or 9 on the first 2 plates, gradually increasing to 

 13 or 14. They are very slender and bluntly tipped. Subambu- 

 lacral spines usually 2, commonly 4.5 mm. (or 2.5 plates) long. A 

 third small spine, about as large as a furrow spine, stands at outer 

 end of series and is sometimes enlarged into a regular suboral; an- 

 other small spine usually stands on the adoral half of the plate, near 

 the above series. Twenty adambulacral plates correspond to the 

 first 10 inferomarginals, omitting the odd plate. 



Mouth plates with 7 or 8 marginal spines and 3 to 5 suboral spines, 

 the latter in a series along the middle of the rather narrow exposed 

 surface, with 1 spine between the innermost spine and the inner 

 aboral corner of the plate. The 2 inner spines of the marginal series 

 are enlarged. 



Madreporic body convex, prominent, situated its own diameter 

 from the marginal plate; striae fine, irregular. There is a tuft of 

 prominent unequal spines on the adcentral side of the madreporic 

 body. 



Variations a7id young. — The type is a very large specimen. The 

 chief differences in the younger examples are: Fewer abactinal 

 pedicellariae (comfined to papular area) ; usually fewer spinelets on 

 abactinal plates; papulae extending to about the inner end of third 

 superomarginal; less conspicuous accessory superomarginal spines; 

 inferomarginal pedicellariae confined to base of ray (in small speci- 

 mens) or interrupted and irregular in occurrence on the outer part ; 

 fewer furrow spinelets (7 to 9 in a specimen with E=80 mm. and 

 a maximum of 11 in another with R=120 mm.) ; as few as 2 actinal 



