44 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 149 



is 7.4 mm. long or only 5 percent of the length of the test. Spines of 

 juveniles, therefore, are more than 4 times as long relative to the size 

 of the test as are spines of large specimens. Similarly, the large adoral 

 spines are proportionately 2.5 times larger on the smallest specimen. 

 Fascioles. — Although the peripetalous fasciole changes little during 

 the growth of the echinoid, the subanal fasciole undergoes a striking 

 change. In the smallest specimen (fig. 13 A) that portion of the 



• 26n 



.22- 



18" 



.16- 



.12- 



.08- 



.04- 



& 



—i — i — i — i 1 — i — i — i 1 — i 1 — r 



20 40 60 80 100 120 

 LENGTH OF TEST 



— 1 1 1 1 i 



140 160 MM. 



Fig. 12. — Scatter diagram showing proportionate decrease in height of periproct 

 with increase in size of test. 



fasciole nearest the periproct is wide, but in a specimen 44 mm. long 

 (fig. 13B) it is much narrower, and finally in a specimen 71 mm. long 

 (fig. 13C) it is completely absent. Mortensen (1951, p. 528) reports 

 the same loss of this portion of the fasciole in Meoma grandis Gray. 



Apical system. — No genital pores are present in the smallest speci- 

 men, but in a specimen 44 mm. long (fig. 14A) three very small pores 

 are present, but none in genital plate 2, the madreporite. In the next 

 larger specimen available, 71 mm. long (fig. 14B), the genital pores 

 are fully open and all four are present. In a large specimen 144 mm. 

 long (fig. 14C), the madreporite is greatly expanded posteriorly, 



