14 Proceedings of the Biological Society of Washington. 



The radial shields are very long, triangular, about half again as long 

 as broad, reaching to the subcircular plate situated on the side of the 

 central plate of the disk ; their distal border is slightly wider than, to 

 twice as wide as, the interradial band of plates ; their inner distal angles 

 are slightly produced and rounded; their outer borders are parallel to 

 those of the adjacent radial shields; their inner borders are in contact 

 distally, proximally diverging very slowly so as to leave a very narrowly 

 triangular area which is occupied by plates. 



The interradial border of the disk, and a patch on the lateral margin 

 is occupied by about a dozen polygonal plates each with a short cylin- 

 drical spine which may have a rounded end, or may bear a few spinelets; 

 these plates extend for a short distance around the outer corners of the 

 radial shields. The interbrachial spaces below are naked except for the 

 few spiniferous plates described above, and numerous minute calcareous 

 spicules. 



In the proximal part of the arm the upper arm plates are six sided, the 

 proximal and distal sides of about the same length, straight, the two 

 lateral sides about twice as long as the two posterolateral sides; in the 

 outer part of the arm they become fan-shaped with a truncate proximal 

 angle. 



At the base of the arm the arm spines are eight in number; the second, 

 third and fourth from the mid-dorsal line are the longest, and the upper- 

 most is nearly as long; these are all webbed to the tip; the fifth is about 

 as long as the first, and has a somewhat enlarged and very thorny tip ; 

 it is united to the fourth by a web which reaches about half way up both 

 spines; the sixth is not much more than half as long as the fifth, with a 

 club-shaped and very thorny tip and no web; the seventh is much shorter 

 and more thorny ; the lowest is in the form of a hook with two strong 

 teeth directed backward toward the mouth ; the hooked character of this 

 spine is fully developed on the second side arm plate. The spinules on 

 the ends of the spines, whenever they occur, are webbed for a greater or 

 lesser distance from their bases. 



The uppermost spine rapidly decreases in length, after about the ninth 

 side arm plate occurring only as a slight spur; on the third or fourth 

 side arm plate the second spine begins to decrease in length, becoming 

 very small at the middle of the arm, so that beyond this point there is 

 only a more or less partial web between the two uppermost spines (origi- 

 nally the third and fourth) and a small spur at the base of the inner. 

 The lower spines remain of about the same relative proportions to the 

 end of the arms, the hook-like character of the lowest becoming more 

 and more pronounced and the next to the lowest tending to assume more 

 or less the same character ; the following spine tends to alternate long and 

 short on succeeding side arm plates. 



The tentacle scale is rather prominent, rounded, spanning the angle 

 between the side arm and under arm plates. 



The tentacles, as contracted in drying, are covered with numerous, and 

 prominent, though very small, papillae. 



