OF WESTERN SIND. 307 



ambulacra is flush with the rest of the test, but the poriferous zone is rather sunken. 

 The pairs of pores are in a simple vertical line, and, although the pairs combine to 

 form triplets, any arching is exceptional; no doubling of the pairs ever occurs. The 

 pairs of pores are rather large for the narrow zone, are wide apart, and unequally so on 

 account of the different sizes of the plates in a triplet. Well-preserved plates show a 

 transverse ridge or narrow rounded-off costa placed aborally with regard to the pair of 

 pores of each plate, and passing not in quite parallel lines from a primary tubercle, or 

 from a large granule in the interporiferous area, to large granules or small tubercles in 

 the interradia. As a rule, two of the costse of a triplet arise from the two adoral plates 

 of the triple combination, or from the part of it which carries the primary tubercle, and 

 one from the aboral member of the triplet, which usually has a large granule on it. 

 There is a vertical row of primary tubercles close to the poriferous zone on either side 

 in the interporiferous areas, and the consecutive broad-based, small-topped tubercles 

 are separated by one or by two large granules. The small mamelon of the tubercle 

 contrasts with the broad sloping boss ; there is no perforation, and crenulation does not 

 occur. But the edge of the expanded base is often indented, for there are the costulate 

 processes which unite the base with the costse over the poriferous zone, and there are 

 sometimes others in the opposite direction, which connect the base with small granules 

 on the same ambulacral plate. Midway between the apical system and the peristome 

 there is, now and then, an extension of a costulate process from the base of one 

 ambulacral tubercle to that of its fellow of the opposite side of the interporiferous 

 area. Here and there there are two large granules, placed transversely, between each 

 tubercle in vertical succession. But near the peristome the oblique costulation over 

 the plates of the interporiferous areas is not seen, and the presence of the pair of 

 intermediate granules is invariable. The ornamentation of this part consists of a small 

 primary tubercle followed by two granules, and this being repeated several times is very 

 characteristic. The arrangement of the ambulacral plates is near the radial end in 

 low primaries, but a little adorally it is in triplets ; the aboral plate of each combina- 

 tion is a low primary plate (that is to say, it reaches the median line) with a slight 

 expansion of the interporiferous portion, and this part carries the granular ornamenta- 

 tion. The next plate, which is of course placed actinally, is a small demi plate, and 

 it is followed adorally by a primary which has a great internal expansion and which 

 prevents the plate immediately above, that is to say the demi plate, from reaching 

 the median line. The last two plates carry the primary tubercle. 



The plates of the ambulacra are therefore very dissimilar, appear crowded, and 

 the sutures are rather sunken and distinct. 



The interradia are remarkable for the angular shape of the adoral edge of the 

 coronal plates, the corresponding aboral parts being indented. The appearance given is 

 that of scale armour, and it diminishes below the equator, where the plates become 

 broader, and not so high as they are near the apical disk. 



The sutural lines of the plates are sunken, and the ornamentation is raised, there 

 being a groove on each plate just below the aboral edge in the median line; whilst the 

 primary tubercle of each plate is in the median line of the plate, and rather towards 



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