OF WESTEEN SIND. 221 



rounding which unites the floor and the sides of the groove ; the pores are small, and 

 have a tendency to become slit-like, especially the inner series. The pores of a pair 

 are separated by a high, prominent, pedunculated granule, which has a slight inclination 

 towards the outer pore in the direction of the apex ; and the pairs of pores are situated 

 in faint oblique depressions. All the pairs are well spaced throughout the zone, but 

 are closer at the apical extremity. The interporiferous area is ornamented with a few 

 minute and widely spaced miliary granules, amongst which a few larger ones are occa- 

 sionally to be found. The anterior pair of ambulacral petals are large, wide, petaloid, 

 situated in deep well-defined grooves, and are rather divergent for the genus. The 

 anterior poriferous zone is bent with a graceful sigmoid curve, and the companion 

 posterior zone is abruptly rounded at a short distance from the apical disk. The 

 poriferous zones in the middle of the petal are very broad ; and the pores are wide 

 apart and slit-like ; they are indistinctly conjugate, and adjacent pairs are separated by 

 a very low and scarcely definite costa, which does not appear to extend beyond the inner 

 half of the zone, or, in other words, only the inner series of pores are separated by 

 it. The interporiferous area is much narrower than the width of the poriferous zone, 

 and is devoid of ornamentation. 



The posterior pair of petals are small, elliptical or subpyriform in outline, with 

 their outer extremity well rounded, and the apical extremity rapidly contracting to a 

 point. The course of the petal from the apex towards the margin is straight, and with 

 no tendency to flexure, and the petals are separated only by the thin narrow ridge of 

 the odd posterior ambulacrum. The poriferous zones are similar in character to those 

 of the anterior petals, but the inner series of pores form a straight line, whilst the 

 outer form the well-developed curve which defines the outline of the petal. There are 

 19 pairs of pores in a zone of the posterior petals against 24 pairs in the anterior petals, 

 the ambulacral plates being smaller and the pairs of pores much closer together in the 

 former. 



The paired interradial areas have all their plates on the abactinal surface more or 

 less gibbous, which produces a vertical series of knobby prominences in each of the 

 columns of interambulacral plates, and these are most conspicuous as they approach 

 the ambitus. On the inner portion of the anterior interradia the two series of promi- 

 nences become merged into one to form the thin, sharp, keel-like ridge that separates 

 the odd anterior groove from the antero-lateral petal ; and at the apical extremity the 

 keel tapers off" gradually to the level of the apical disk. There is a similar keel at the 

 apical extremity of the lateral interradia, but it is short, narrow, flat on the upper 

 surface, and likewise tapers down to the level of the apical disk. The keel of the odd 

 posterior interradium, which is narrow, rather high and ridge-like, gradually expands 

 and disappears over the summit of the oblique posterior truncation. The general area 

 of this truncation is concave, and the margins on the lower half are defined by 

 gibbosities on the plates, which are also present on the plates of the tumid inferior 

 prominence beneath. 



The periproct is comparatively small, vertically elliptical, and is placed at the 

 summit of the concave posterior truncation. 



2g 



