38 THE FOSSIL ECHINOIDEA 



The well-preserved specimens indicate clearly that they have a most elaborate raised 

 ridge-like ornamentation, and no sutural depressions and penetration ; and the badly- 

 preserved ones have the appearance of deeply-bevelled sutures, and as if the test had 

 been cut out, instead of added to, in thickness. 



Genus DICTYOPLEUEUS, gen. nov. 



The test is small, hemispherical above, slightly concave below, with a small 

 peristome and small cuts. The pairs of pores are in continuous straight series. The 

 tubercles of both areas are very small. Those of the ambulacra are in two vertical 

 series close to the pores, and each tubercle is united by a vertical raised ridge with 

 those above and below, and by a zigzag of raised ridges with those of the other 

 vertical series opposite. The tubercles of the interradial areas, in two vertical series, 

 are on vertical raised ridges or ribs. Each tubercle is continuous with two of the 

 opposite series by a raised ridge, and sends oflf two or three ridges to the poriferous zone. 

 The tubercles are faintly perforate and slightly crenulate, and there are indications of a 

 few secondaries around them. The perforation and crenulation is indistinct in the ambu- 

 lacral areas. Here and there the narrow raised ribs have small granules upon them. 

 The sutural lines of the plates are distinctly seen, and there are no depressions or 

 penetrations of them. The apical system, obliquely placed, is elongate; and one 

 ocular plate enters the anal ring. 



1. DiCTTOPLEUEUS ziczAC, Duncau & Sladen. Plate IX, Figs. 1-3. 



The test is small, hemispherical above the rather tumid ambitus, which is cir- 

 cular in outline, and slightly concave actinally, where there is a small sunken peri- 

 stome with slight cuts. 



The apical system is large for the size of the test, is placed obliquely, and the 

 anus is elongate and elliptical in outline. The direction of the long axis is as in 

 an Echinometra. The ring of generative plates is narrow ; and one ocular, the right 

 posterior, enters into the composition of the anal ring. The madreporic body rises 

 like a small knob, and its plate is the largest ; none of these plates enter far into the 

 interradial areas. The ocular plates have triangular depressions on their sutures on 

 either side of a vertical line, and the pore is visible near the apex of the blunt angular 

 projection. 



The ambulacra, about one half of the breadth of the interradials at the ambitus, 

 have two vertical series of small tubercles on narrow, raised, rounded ridges, placed 

 close to the poriferous zones. The tubercles are small, very faintly perforate and 

 crenulate, and they increase in size and number actinally. The interporiferous zone is 

 crossed by a zigzag of raised ridges, which unite the opposite and alternate tubercles 

 on the vertical ridges. Much of the surface of the plates is seen on either side of the 

 ridges, and the sutural lines are distinct ; these cross over the ridges in young specimens. 

 The pairs of pores are in single rows, and there are three pairs opposite each interradial 



