OF WESTERN SIND. 289 



grooves passing from these outwards and slightly downwards, to cross the sutures of 

 the radial plates on either side. Then comes the pore, with or without a raised rim, 

 and there may be granules adorally to the pore. 



The ornamentation of the radial plates is mainly continuous with that of the 

 basals on either side. On a fully developed radial there is a central discontinuous ridge, 

 broken up here and there into elongate and conical granules, ending adorally in the 

 projection already noticed as having a relation to the optic pores. On either side of this 

 vertical ridge and granule-tract are two or even three ridges and grooves, placed 

 obliquely, and corresponding with the basal structures. Usually a ridge is near the side 

 of the radial plate, and it may have no relation to a basal one. 



The ambulacra are well developed, are tumid, and project more than the interradia 

 above the ambitus, have a few small primary tubercles abactinally reaching up to the 

 radial plate, and carry very large primaries at the ambitus and just below. Petaloid 

 above, the ambulacra are rather broad at the peristome, and nearly as much so as the 

 interradia ; moreover, the peristomial margin has a rather deep concavity between the 

 last pair of tubercles ; and there are slight cuts on either side of the ambulacra, which 

 are deeper than the concavity just mentioned, and a part of a cut and of the tag that 

 passes up from it, externally to the pores, belongs to an ambulacrum. 



On the abactinal surface, at the level of the third and of the fourth interradial 

 plate, the ambulacra are slightly narrower than the interradia; at the ambitus the 

 difference is less, especially in full-grown specimens. 



The poriferous zones are broad and nearly straight down to the first large 

 tubercle, and then they become exceedingly irregular and form a series of arcs 

 with the concavity towards the tubercles; but near the peristome there is a 

 disposition to form oblique series. There are no extra plates near the peristome, 

 and throughout the zones there is an arrangement in triplets, except close to the 

 radial plate. 



The plates of the ambulacra, in their poriferous parts, are large and broad ; they 

 are of nearly equal height near the radial end, and increase in height to the ambitus. 

 There is a still greater increase in height in the plates of the triplets of the great 

 tubercles, and a gradual diminution of those below the last great tubercle down to the 

 peristome, where the plates are very low. 



The pairs of pores are large after the second pair ; they are wide apart vertically, 

 and there is an obliquity in their direction, even very high up in the ambulacrum, and 

 this becomes decided at the ambitus. The pores are usually large and wide apart ; but 

 they are smaller and closer near the peristome, where the aboral pore of each pair is 

 placed much higher in the plate and only a little to the outside of the adoral pore, 

 which occupies the usual position at the lower suture of each plate. There is a rapid 

 diminution in the size . of the plates and of the size of the pores near the peristome ; 

 but the plates are broad there, extend into the tag, and the pores are remote from the 

 outer or interradial suture. 



The interporiferous area is narrow near the apex, increases gradually to the part 

 of the tumid circumference where the diameter of the test is the greatest, and then 



2b 



