284 ON SOME NEW AUSTRALIAN ECHINI. 



much better defined, broad above, gradually narrowing below, 

 and joins in a beak the elongate actinal plastron. The central 

 line of the actinal plastron forms an angular keel which is 

 prominent for the posterior half only. The actinal surface is 

 slightly convex and gradually rounded and raised at the ambitus. 

 It is rather flat anteriorly, but slopes upwards from the keel on 

 the plastron posteriorly. At that end it is gradually rounded, 

 and without forming a distinct ambitus passes to the vertical face 

 of the anal end. The actinosome is very large transversly, 

 nearly equalling one-third the width of the test. It is crescentic, 

 the posterior lip a little prominent. The bare ambulacral 

 avenues are connected round the actinosome, forming a bare 

 anterior space extending into an obtuse point on each side of the 

 test and about one-sixth of the whole width from the edge. The 

 anterior lateral phyllodes become narrow gradually from the 

 actinosome and are scarcely apparent near the subanal fasciole. 

 Bound the mouth the pores are regular and close, situated on the 

 edge of a large oval scrobicular area. At the faint anterior 

 sulcus they are interrupted, and one or two pores are visible on 

 the sulcus itself. They become scattered and disappear a little 

 below the actinosome. Outside the phyllodes they are large, 

 close, with a distinct raised area, not perforate, and gradually 

 decreasing in size towards the ambitus, above which there are 

 nothing but miliaries. The abactinal surface is convex, with an 

 equal inclination upwards towards the peripetalous fasciole : 

 inside this it is suddenly much more raised towards the apex, 

 which is a conspicuous broad protruberance just about the 

 anterior transverse petals, and anterior to the reproductive 

 system. The whole abactinal surface is covered with miliaries 

 of uniform size. There is no anterior sulcus, but with a lens a 

 narrow zigzag interrupted grove may be traced along the mesial 

 line. Below the ambitus a faint wide depression is visible. 

 From the genital pores to the anal orifice there is a distinct 

 depressed slightly undulating sutural line. The fasciole is rather 



