156 Proceedings of the Biological Society of Washington. 



responding superomarginals, and the following inferomarginals are situ- 

 ated considerably beyond the corresponding superomarginals, though not 

 enough so as regularly to alternate with them. In general the infero- 

 marginals agree approximately in size and in shape to the corresponding 

 superomarginals. They bear a large stout spine situated near the upper 

 border, somewhat stouter than the spine on the superomarginals, and 

 reaching 5 mm. in length; below this is another spine, about half as long 

 and correspondingly less stout, and below this another, shorter and still 

 more slender. The sides of the inferomarginals are armed with long 

 scattered spinules a few of which occur also on the outer surface ; one or 

 more of these may be more or less enlarged. The interradial infero- 

 marginals bear a column of five or six approximately equal spines, resem- 

 bling the longest spines in the similar corresponding supermarginal 

 series ; the first inferomarginal bears three spines of which the uppermost 

 is the longest and the others decrease in length; the second and third are 

 similar, but with progressively greater difference between the elongate 

 uppermost and shorter lower spines. The lower borders of the infero- 

 marginals in the interbrachial arc are prominent, raised above the surface 

 of the actinal intermediate plates, and spineless. 



Pectinate pedicellariae occur between the interradial pair of supero- 

 marginals, or between one of these and the adjacent superomarginal, in 

 one case in both situations ; there are no other pedicellariae in the supero- 

 marginal series. 



In three cases I found small pectinate pedicellariae between the infero- 

 marginals; one was between the two interradial inferomarginals, one 

 between one of these and a second inferomarginal, and the third between 

 a third and fourth inferomarginal. 



On the disk pectinate pedicellariae may replace the central spine in the 

 paxilte, but these are relatively rare; more frequently pectinate pedicel- 

 lariae are formed by the modification of the borders of two adjacent 

 paxillae; this type occurs also on the arms. 



The actinal intermediate area is covered with about thirty crowded 

 plates which decrease rapidly in size from the adambulacrals to the 

 marginals; these are armed with one, or in some of the larger two, long 

 spines, and from one to six scattered elongate spinules. One or two 

 pectinate pedicellariae occur between these plates, in the angle near the 

 mouth plates. There are from eight to ten actinal intermediate plates 

 adjoining the adambulacrals; these correspond to seven adambulacrals, 

 and the series ends at the proximal border of the fourth inferomarginal. 

 Most of these plates have pectinate pedicellariae between them. 



The adambulacral plates are at first about as long as broad, the inner 

 half projecting into the ambulacral groove in a right angle ; further out 

 on the arm they gradually become broader than long, and the projecting 

 angle gradually becomes more acute. The armature consists of seven or 

 eight long furrow spines, the two central the longest and stoutest; on the 

 actinal surface there are two long stout spines, much longer than the 

 furrow spines, resembling the lower spines on the inferomarginals, of 

 which the inner is usually slightly stouter and longer than the outer ; 



