334 HAWAIIAN AND OTHER PACIFIC ECHINI. 



Ambulacra decidedly wider than interambulacra; primary spines greenish, more 



or less extensively tipped with red porosissimus. 



Ambulacra not appreciably wider than interambulacra and usually distinctly 



narrower; primary spines vary from very pale brown to reddish purple . . . inflatus. 

 Interambulacral plates very numerous (30 in specimens 22 mm. h. d., 40-50 in speci- 

 mens over 36 mm. h. d.), their tubercles large, areolae of primaries occupying 

 nearly whole height of plate and hence forming more or less crowded vertical series 

 on each side of interambulacrum; primary spines whitish or cream color, or pale 

 purplish or greenish, often tipped with lighter or darker; ambulacra in adults 

 usually distinctly wider than interambulacra pycnolylus. 



Holopneustes pycnotylus, 1 sp. nov. 

 Plates 104, fig. 4; 112, figs. 6-9. 



~ The form of the test in this species shows great individual diversity, appar- 

 ently not associated with age. The type (PI. 112, fig. 6) is not quite 36 mm. in 

 diameter, and is 32 mm. high, the height thus equalling .90 h. d.; the ambitus 

 is circular. Another specimen (PI. 112, figs. 8, 9) also with a circular ambitus, 

 is 33 mm. in diameter and only 25 mm. high; the height is thus only about .75 

 h. d. A specimen 23 mm. in diameter is 19 mm. high (v. d. = .83 h. d.) while 

 another almost as large is only 16 mm. high (v. d. = .71 h. d.). A specimen 

 (PI. 112, fig. 7) 34 mm. in diameter and 30 mm. high has the ambitus very 

 distinctly pentagonal. In a specimen 19 mm. h. d., there are 26 interambulacral 

 and 49 ambulacral plates in each column; in another, 23 mm. h. d., the numbers 

 are 30 and 55 respectively; in another, 33 mm. h. d., 45 and 88; in another, 

 34 mm. h. d. (pentagonal) 37 and 76; in the type, 36 mm. h. d., 38 and 90; and 

 in another, 37 mm. h. d., 52 and 113. The relative width of ambulacra and 

 interambulacra shows some diversity also. Thus the same six specimens give 

 the following measurements, the ambulacral width being given first : 6 and 6, 7 

 and 6.5; 11 and 8; 10 and 10; 11.5 and 10; 12 and 10. The ambulacra are thus 

 on the average about 15% wider than the interambulacra. The abactinal system 

 and actinostome are small, the latter averaging about .30 h. d., while the abacti- 

 nal system is only half as large. The poriferous areas (PL 104, fig. 4) are wide, 

 each one at least half as wide as the interporiferous area, and in adults the propor- 

 tion rises to three fourths or even four fifths. The arrangement of the pores and 

 tubercles is as usual in the genus; there is a more or less perfect vertical series 

 of pore-pairs on each margin of the poriferous area and between these are numer- 



= crowded + TvXos = a tubercle. 



