194 THE FOSSIL ECHINOIDEA 



the size of the pores and the distance between adjacent pairs is greatly increased. Near 

 to the fasciole the pores again become smaller, and outside its boundary are simply 

 microscopic. The floor of the groove is covered with small low granules of two sizes, 

 irregularly interspersed and rather widely spaced. 



The antero-lateral petals are large, long, and in deep grooves. They have a very 

 straight appearance, the breadth being comparatively uniform, and the expansion towards 

 the outer extremity only slight. The groove does not terminate abruptly at this point, 

 but contracts gradually, which gives to its outer end rather a pointed character. The 

 divergence of the antero-lateral petals is great, the angle enclosed being about 120°. 

 The poriferous zones are wide, the pores large and elongately pyriform, with the 

 pores of a pair united by a shallow furrow, the intervening ridge being broad, and orna- 

 mented along its median line by a single row of small miliary granules. There are 

 about 33 pairs of pores in each zone. The interporiferous area is very uniform in 

 breadth, excepting at the apical extremity, where it narrows rapidly ; its normal breadth 

 is about equal to that of the poriferous zone at its widest part. The apical portion of 

 the posterior zone is more precipitous than any other part, and the anterior zone is, on 

 the whole, rather more precipitous than the companion zone, although both zones 

 occupy entirely the lateral walls of the groove. The only ornamentation on the inter- 

 poriferous area consists of a few very minute, very widely and irregularly placed 

 miliary granules. The antero-lateral petals measure 25 miUim. from the centre of 

 the apical disk to their extremity, and are 6 millim. wide at their broadest part. 



The postero-lateral ambulacra are four fifths of the length of the anterior petals, 

 measuring 20 millim. long and 4-5 millim. broad. They are in deep grooves, similar to 

 those of the anterior pair, and they do not expand greatly in width. The petals curve 

 rather sharply inward at the apicat extremity, and the posterior zone is more curved 

 than the anterior zone, its contour being sigmoidal, in consequence of a rather rapid 

 bend outward at the outer extremity, whilst the outline of the anterior zone is a simple 

 curve. There are about 29 pairs of pores in each zone, and their character is similar to 

 that of the anterior petals above described. The posterior are much less divergent than 

 the anterior pair of petals, the angle they enclose being about 60°. 



The anterior interradia have the appearance of forming a high tabular keel, in con- 

 sequence of the deep ambulacral grooves and the gently rounded slope of the interradia 

 to their margins. At the apical extremity this apparent carination is bevelled off to the 

 level of the apical disk. Each of the plates of the interradial areas is slightly tumid, 

 which imparts a rather knobby character to the test, the feature being most marked in 

 the plates just above the ambitus. The lateral interradia are higher and rather more 

 carinate in appearance at the apical extremity, although they are bevelled off in the 

 neighbourhood of the disk in the same manner as the anterior areas. The odd posterior 

 interradium is narrow, high, and prominently convex, forming a regularly rounded 

 saddle-back, whether viewed transversely or longitudinally, the apical portion sloping 

 down gently to the level of the apical disk. The posterior character of the odd inter- 

 radium immediately above the periproct is much damaged. The margins of the test 

 are tumid and well rounded on to the actinal surface, excepting perhaps posteriorly, 



