,332 KCHINODISCUS BIFORIS. 



are rounded at the extremity, closed ; the poriferous zones are broad, equal- 

 ling in width the interporiferous space. 



The lunules are more or less closed, or simply form open slits, extending 

 over one third the distance of edge from the apex towards the centre, in 

 prolongation of the median longitudinal axis of the posterior pair of petals. 

 The tuberculation of the upper surface is small, compact, of uniform size, 

 carrying minute, short, line spines, slightly clavate. Tin' median interam- 

 hulacral and amhulaeral spaces are covered with larger and more distant 

 tubercles, decreasing in size near the edge, carrying longer and stouter 

 spines. The interambulacral spines are more brilliant 1\ colored than the 

 amhulaeral. The amhulaeral furrows are not deeply grooved ; the posterior 

 pairs branch more frequently near the edge than the others. The mouth 

 is nearly central, slightly anterior. The anus is of irregular outline, more 

 or less circular, placed in a line with the inner extremity of the cuts. The 

 color of dried specimens is violet or reddish-brown as they become older, to 

 judge from dried specimens. 



Half the internal cavity is occupied by a close net-work of pillars, occupy- 

 ing the whole space from the edge ; between the commencement of the pil- 

 lars and the slender auricles the whole actinal floor is covered by a succession 

 of elongated cells, of the most irregular shapes, formed by the rising of thin 

 lamella 1 or ridges from the floor, which form eventually the pillars extending 

 to the upper floor, as is readily seen on examining the base of the innermost 

 row of pillars, arising directly from the continuation of the walls of those cells 

 which have risen sufficiently above the lower floor to form pillars, and to 

 reach the upper floor. The net-work across the amhulaeral spaces is reduced 

 to short low ridges, running at right angles to the amhulaeral tubes. 



Long Trans. Length Post. Width [ntcrp Length Length Dlst Amu Dlst. Mouth 



Uiuui Diain. I'.nr IVt;ds. Pol /..me. Zone. Odd IVtaL Luuulc. from Edge, from Aut. Edge. 



133. 139. 2G.2 4. 4.1 30. 30. 30 1 G4.5 



155. 157. 30.1 3.t) 5.2 35. 38.5 32. 72.1 



Zanzibar ; Philippine Islands. 



Ecbinodiscus biforis 



EcJiinodutcus bisperforatus Lkske. 1778. Kl., Add. 



I Echinodiscus biforis A. A.,.. 1872, Rev. Ech., Pt I. p. 113. 



PL XIII". f. o-6 ; PL XXXVII f. 4-6. 



The outline is irregular, narrower anteriorly, rounded and slightly indented 

 opposite the anterior lateral ambulacra. Greatest breadth about half-wry 



