254 THE FOSSIL ECHINOIDEA 



2. CffiLOPLEUEUS Pratti, d'ArcMac & Haime. Plate XXXIX, Figs. 9-12, 



Tlie following is the diagnosis of MM. d'Archiac and Haime {op. cit. p. 199) : — 

 The test is subcircular and moderately high and rather convex above ; periproct rather 

 small, and the generative pores large and opening in the middle of the genital plates, 

 which are rather longer than broad, and slightly angular externally. Ambulacral areas 

 three fourths the breadth of the interradia. Pores in rather close pairs, which form in 

 the actinal half short series of slightly inclined triplets. The pores are large, circular, 

 those, of the same pair nearly horizontal, separated by a broader space abactinally than 

 actinally. Twelve ambulacral plates for each vertical series, almost as high as broad, 

 and pierced by three pairs of pores ; their internal two thirds are occupied by a large 

 projecting primary, and there are fine granulations on the sutural lines. The interradia 

 consist of twelve plates, which are usually twice as high as broad. They have a vertical 

 line which is granular and projecting, which limits the abactinal smooth median area, 

 and which actinally divides the plates in half; the internal part there is covered 

 with a large tubercle, and the outer with a moderately large tubercle and a smaller one 

 external to it. All the tubercles are imperforate and non-crenulate, and stand on a 

 thin base. The long diameter is 32 millim., and the short 2 millim. less. Height 

 19 millim., peristome 12 millim., periproct 3 millim. 



Only one, much altered specimen, was seen by MM. d'Archiac and Haime; but 

 the examination of the specimens from the Nari series indicates that their diagnosis is 

 correct in the main. 



The following observations are recorded as the results of our study of the numerous 

 specimens forwarded from India. They are taken in the order of the diagnosis given 

 above : — 



1. The shape is circular in outline actinally, but the projection of the ambulacra 

 abactinally gives a pentagonal appearance which becomes less with age and size. The 

 convexity above is well seen along the ambulacra. 



2. The apical system is large. The periproct is oblique, its longest axis being 

 in the direction of a line traversing ambulacrum No. 1 and interradium No. 3 

 (Loven) ; it is rather large in relation to the diameter of the test. The basal (gene- 

 rative) plates are not quite equal in size, the madreporite being the largest ; their 

 outer edge is a blunt angle (about a right angle), and it projects decidedly into the 

 interradium. The madreporite fprms a sharper angle. The aboral edges of the 

 plates form a raised ring around the periproct, and it carries a close row of 

 large miliaries. Each plate has a prominent tubercle on it, and just external to 

 it is the generative pore, which is large, a little external to central. The pore 

 of the madreporite is nearer the margin of the plate. The radial (optic) plates 

 are large; their inner or apical part is formed by two curved edges joining at a 

 very open angle ; their sides also curved, concavity outwards, slope, but so as to 

 make the curved (concavity actinally) adoral edge broad; this broad curve has a 

 minute central projection, and under it is the double optic pore. In some specimens 

 the double foramen is visible a little way from the adoral edge on the surface of the 

 plate. It is in a curved depression. The distance from the periproct-edge to the 



