24 HAWAIIAN AND OTHER PACIFIC ECHINI. 



length; anterior petals more than .80 as long as unpaired one; 

 lower surface not usually markedly concave, though mouth is 



distinctly sunken japonicus. 



Size small, not exceeding 75 mm. in length; width usually not .80 



length; anterior petals short, scarcely .75 as long as unpaired 



one; lower surface strongly concave. 



Unpaired petal widely open, with numerous pore-pairs (36 on 



each side in petal 10 mm. long); petaloid area not at all 



depressed lytopetalus. 



Unpaired petal nearly closed, with fewer pore-pairs (28 on each 

 side in petal 14 mm. long); petaloid area in adult more or less 

 depressed, at least the distal portion lying lower than the thick- 

 ened test-margin though the apical system may be much higher relicvlatus. 

 Test rather low (v. d. = .15-. 22 test-length), with thin margins (.04-.08 

 test-length); aboral surface more or less flat distal to petals; lower sur- 

 face flat or slightly and gradually concave. 

 Primary tubercles numerous, small; on each ridge between pore-pairs 

 of unpaired petal, there is a single regular series of 6-15; unpaired 

 petal with poriferous areas converging distally though petal may 

 remain open. 

 Unpaired petal with relatively few pore-pairs (about 50 on each side 

 in a petal 40 mm. long); median area of petals markedly 

 obovate, narrow proximally and broadest distally; poriferous 

 areas converging rather abruptly, and tending to close the pet- 

 als, especially the anterior and posterior pairs humilis. 



Unpaired petal with more numerous pore-pairs (60-70 on a side in a 

 petal 40 mm. long); median area of petals not obovate, usu- 

 ally as wide at the middle as anywhere; petals more or teaE 

 open. 

 Test about .90 as wide as long or wider; anterior lateral pi 

 about .90 as long as unpaired petal. 

 Unpaired petal broad and widely open; its breadth is de- 

 cidedly more than half its length and it is at least twio 



widely open as posterior pair prostratus. 



Unpaired petal narrower with poriferous areas more con- 

 vergent; its breadth seldom exceeds half its length and IB 

 usually less; it is sometimes widely open but not mor 



than posterior pair rotundus. 



I • ii about .80 as wide as long; anterior lateral petals short, only 



about .80 as long as unpaired one subdepressus. 



Primary tubercles scattered, rather large especially on interambulacral 

 areas orally; on each ridge between pore-pain of unpaired petal, 

 there an- not more than four and often there is only one or none: 



unpaired petal short, only .25-.30 test-length, with poriferous an 

 parallel or Bomewhal diverging (in small specimens somewhat 



convergent). 

 Primary tubercle- and their .-pirns orally not strikingly peculiar; 

 petals (at least in adults) much wider than half their length. 

 Test .90-.95 as wide as long, not depressed at distal end of 



petals; color, yellowish brown incoming deep green after 



