404 BULLETIN lOO, UNITED STATES NATIONAL MUSEUM. 



sixteenth plate there is but a single plate between the inferomar- 

 ginals and adambulacrals. This single longitudinal series persists 

 to within about 12 mm. of the tip of ray. Between the first and 

 seventh inferomarginals the number of plates in the transverse se- 

 ries decreases from 6 to 2. The whole actinal interradial area 

 proper is very small, as half of the actinal surface of the disk is 

 occupied by " abactinal " plates. 



If a portion of the abactinal skeleton is denuded and cleared the 

 irregular plates of the median portion of ray are seen to be mostly 

 3-lobed and very strongly but irregularly imbricated. The plates 

 themselves are not of uniform size and scarcely 2 are of exactly the 

 same shape. The dorsolateral plates, on the contrary, are regularly 

 4-lobed and the proximal longitudinally directed lobe overlies the 

 corresponding distal lobe of the next plate adorad, while the trans- 

 verse lobe directed toward the radial line overlaps the external lobe 

 of the next plate. The dorsolateral papulae occupy singly the small 

 interspaces and are consequently in regular longitudinal and trans- 

 verse series. 



Adambulacral plates small, close- set, with a slightly curved fur- 

 row margin. The adjacent actinal intermediate plate encroaches 

 upon the surface which is usually a little longer than wide. Fur- 

 row spines proximally 5, the 3 median 3-sidcd or quadrate in section, 

 round-tipped or truncate ; the proximal and distal spines are shorter ; 

 usually the distal is about one- third or one-half as long as adjacent 

 spine and the proximal about one-half or three fourths. The first 

 few plates usually have the spines more flattened at the end. Occa- 

 sionally there are 6 spines and distally usually 5 or 1. Just back of 

 the furrow spines (which stand upright) are 3 or 4 shorter spinelets 

 with thicker ends, and back of these about 3 or 4 slightly smaller 

 spines, which stand so near the actinal intermediate plate that it is 

 difficult to determine sometimes to Avliich plate they belong. The 

 plates at about the middle of ray have 3 or 4 longitudinal series of 

 spines, 2 or 3 in each series. The adambulacral spines are ail blunt, 

 very close-set, and they grade from the furrow spine into the actinal 

 intermediate spines. 



Mouth plates very small with nearly straight furrow margin bear- 

 ing 5 to 7 compressed furrow spines with broad tips and edge 

 to furrow, heavier than the adambulacral spines, and increasing 

 slightly in length toward the inner angle. Behind these on each 

 plate is a row of 4 or 5 smaller subambulacral spines which occupy 

 about all of the remaining surface of the plate. 



Madreporic body small, surrounded by 6 plates of which 1 on 

 the adcentral side is largest, and situated slightly adcentral to the 

 middle of r. 



