OF WESTERN SIND. 35 



half of the interradial area. The ambulacra are narrow, and are convex from side to 

 side. There are a few primaries in the interporiferous zone. They are small at the 

 apical end, enlarge gradually towards the ambitus, and cover much of their plates there. 

 They are in two alternate vertical rows, and have broad bases, tumid bosses, and small 

 mamelons. The bosses are crenulate, and also ridged down their flanks; they are 

 upon slightly raised areolae, which are marked with linear depressions and intermediate 

 ridges in connexion with the poriferous plates. The sutures between the plates of the 

 interporiferous zones are distinct ; and between them and the base of the mamilliform 

 processes are a few large miliaries in an incomplete circle, and they are sharply pointed 

 or nodulose, and are usually oblique in their direction. The crenulation takes on the 

 form of nodules more or less sharp, and ridges with intermediate furrows, and there 

 may be pointed granules on the bosses. The small mamelon has a constricted neck 

 and is imperforate. 



Every plate of the interporiferous zone has not a primary tubercle on it, and there 

 are small wedge-shaped plates between the tubercle-bearing ones in vertical series. 

 Hence the tubercles are rather wide apart, one above the other. The intermediate 

 plates are furrowed at their edge in the direction of the poriferous plates, and they have 

 a few oblique and sharp-pointed miliaries on them. They have well-marked sutures, 

 and are comparatively smaller at the ambitus than near the apex. 



The poriferous zones are narrowest actinally, and slightly largest near the apex ; 

 they are placed obliquely on the test, on the lateral slopes of the ambulacra. The 

 number of plates is considerable, and there are from 10 to 17 in contact with the 

 larger interradial plates. The pores are crowded vertically, but only form a double 

 series near the apex, although there is much close alternation or serial succession 

 elsewhere. Near the actinostome they are in single vertical series. They are conjugate, 

 small, slightly elliptical or round ; and each plate has raised margins above and below, 

 which form between them hood-shaped openings and tubular furrows. These margins 

 become broken ridges in some places, and may have a miliary tubercle upon them. The 

 number of pairs diff'ers in relation to the primary ambulacral plates, and there are often 

 five or eight pairs. 



The interradial areas are large, have their sutures very visible, the median space 

 sunken, and the projecting centre of each plate occupied by a very projecting large 

 primary, which is flanked by a surface on which are placed a few spiniferous large 

 miliaries, and some small miliaries here and there. 



The bosses are placed on raised scrobicules, surrounded by a more or less complete 

 circular furrow ; they are tumid cones, with a broad apex and wide base, are furrowed 

 and ridged on the flanks, and crenulate and nodular above. The mamelon is small, has 

 a tall constricted neck, and is therefore high ; it is imperforate. There are eight plates 

 from the ambitus to the apex, in each half of the area ; and they are very broad near the 

 margin, and diminish in breadth, and increase slightly in height, towards the apical 

 system. 



The length of the test is ys ^^^^ J the greatest width of the ambulacra -3^, and of 

 the interradial areas -^o inch. 



