288 THE FOSSIL ECHINOIDEA 



the edge of the peristome is at a higher level than the surface just mentioned. The 

 breadth of the test greatly exceeds the height, and the contour from above is nearly 

 circular, an apparent angularity being sometimes given by the projecting tubercles of 

 the ambulacra. From below the aspect is circular at the narrowing part. 



The apical system is on the top of the low slope upwards, from the widest part of 

 the test ; it projects with a different slope from that of the test below, and is well 

 developed. The periproct is large, somewhat elliptical, its long diameter being between 

 interradium no. 3 and ambulacrum no. 1. The basals are large and form the anal 

 ring; they are slightly raised into a marginal ring which is ornamented with a 

 continuous row of close granules, and they are perforated for the ovarial duct, either at 

 mid-distance between the periproct and their adoral angle, or in the outer third of 

 their length. The pore is large and may or may not have a raised rim. The adoral 

 angle of a basal extends well into the interradium, and only slightly more adorally than 

 the radial plates close by. 



The greatest breadth of a basal plate is at a little distance from the anal edge, and 

 all the sides are slightly and symmetrically concave, and the three angles on either side 

 of the plate are distinct and moderately open. The madreporite is in the largest plate. 

 The radial plates are large, broad as a rule, broader than high, and the sides, which are in 

 contact with the basals, are slightly outward curving, whilst the adoral sides are slightly 

 concave. The adoral edge is concave, and has a centrally downward projecting and 

 more or less sharp granule, which is continued on to the upper surface of the plate as 

 a part of the ornamentation, and also downwards and inwards so as to separate the 

 optic tract into two parts. Hence there is no pore on the surface of the radial plate, 

 but there are two, one on each side of the inwardly projecting process at its adoral 

 edge, and they are more or less hidden. The outer angles of the radial plates corre- 

 spond with the position of the second pair of ambulacral pores. In some radial plates 

 there is a double curve at the adoral edge, and then the process occupies the inter- 

 mediate projection. The radial plates never enter the anal ring. 



The apical plates are thick and closely sutured, and it may be noticed in some 

 specimens that there is a furrow over each suture which is crossed or not by the ridges 

 and furrows of the ornamentation. The ornamentation of the apical system is of large 

 granules, some solitary and bluntly conical, others in series, and most more or less 

 united to form ridges with intermediate furrows. The ornamentation radiates laterally 

 from a greater or less tubercle of the third order, which is on each basal plate between 

 the genital pore and the granular rim of the plate. There is often a little group of 

 granules at this spot and it forms a centre of radiation. Several ridges and inter- 

 mediate grooves pass outwards and slightly adorally, cross the basal plate to its outer 

 edge, and become continuous with a series of ridges and grooves which are upon the 

 contiguous radial plate. Usually there is little or no ornamentation on the basals 

 adorally to the pore ; but there are exceptions to this, and there may be a row of small 

 miliaries close to the edges of the plate. The ornamentation of a fully developed basal 

 plate consists of the row of nearly separate granules close to the anal edge, a few small 

 granules a little adorally to these, a tubercle of the third order, and lines of ridges and 



