C. L. Edwards 
271 
K. Stone-canals and Madreporites. 
As a rule the stone-canals appear in two tufts, one slightly ventral of the base 
of each dorsal radius (Fig. B, R St C and L St C). In some cases from 1 — 7 
stone-canals are separated in a line extending to 10 mm. from the dorsal mesentery. 
Figs. C— F. Stone-canals and madreporites. C, cylindrical; D, spherical; E, pear-shaped; 
F, profile of E. x 5 J . 
In the majority of cases the madreporite is cylindrical (Fig. C), less frequently 
spherical (Fig. D), or pear-shaped (Fig. E). The head is compressed from side to 
side, presenting a narrow profile (Fig. F). 
Figs. G, H. Cylindrical madreporites. G, partly twisted; H, twisted iu a spiral, x 8. 
Often a cylindrical madreporite is twisted upon itself (Fig. G), or even has as 
many as 4 or 5 turns of a spiral (Fig. H), and frequently the stone-canals are 
twisted. 
At times 2 madreporites are joined together. In 16, six such united pairs 
occur in the left tuft. In other individuals 3, 4 or 5 madreporites may be fused, 
