io Bulletin 26 94 



The ambulacral areas are broadest at the ambitus, and their 

 surfaces are ornamented with mammillated, crenulate, perforate 

 tubercles arranged in transverse rows of two to three tubercles 

 on each half of the ambulacrum, alternating with similar rows 

 on the opposite half. This number may be reduced to one 

 on each half ambulacrum in very small specimens. Around each 

 couplet or triplet of tubercles there is a ring of granules. This 

 ring does not seem entirely to close each areola, but shows only 

 a tendency to do so between the tubercles. 



The pores are round and uniserial or moderately arched 

 and separated by granules. Below the ambitus, they become 

 crowded and irregular. 



The interambulacral areas are broad, being four or five 

 times as wide as the ambulacral areas. The median portion 

 is somewhat depressed, leaving the area in rounded, inflated 

 halves. The surfaces of these areas are ornamented with alter- 

 nating arched rows of mammillated, crenulate, perforated tuber- 

 cles numbering from 3 to 11 on each half area. This number 

 varies according to the age of the individual. In the small speci- 

 mens, there appear to be only three tubercles, in each row, but 

 in the larger ones the number increases to 10 or 11. This variabil- 

 ity extends to the ambulacral areas as well, although the specimen 

 figured in Plate IV, figure 7 shows a persistence in two tubercles 

 to the row. This is a small individual considerably magnified 

 in the figure. Encircling each areola is a ring of granules. These, 

 and the granules on the ambulacral area, are so arranged that 

 they appear at first sight as a double row of granules between 

 the rows of tubercles. Toward the apical system and the peris- 

 tome, the number of tubercles is reduced, and in the region of the 

 peristome some crowding occurs. 



The peristome is relatively small, decagonal, and notched. 

 The ambulacral and interambulacral lips are straight, but the 

 latter are about one-half of the width of the former, measured 

 from notch to notch. 



The apical system consists of five subtriangular genital plates 

 and five V-shaped ocular plates so arranged that they form a 



