OF WESTERN SIND. 71 



numerous, and are crowded near the apex in consequence of the narrowness of the 

 arabulacral plates ; and the pairs are separated by costal ridges, distinct in some parts 

 and. sparsely and irregularly ornamented with granules (Fig. 6). 



The antero-lateral ambulacra are petaliform, slightly open, and are as long as 

 but broader than the anterior odd ambulacrum. The poriferous zones are curved and 

 even slightly sinuous distally, especially the posterior ; and the interporiferous zone is 

 broader than that of the other ambulacra. The posterior lateral ambulacra are the 

 longest ; they are nearly closed, form an acute angle, and reach back to within one and 

 a half times their length of the periproct. The inner or posterior poriferous zones are 

 narrow and nearly straight ; and the outer are much the broadest and curved ; the 

 distinction between the two zones is very decided. All the ambulacra are nearly flush 

 with the test, and their interporiferous zones are covered with a small tuberculation 

 resembling that of the interambulacra of the upper part of the test. The tubercles are 

 minute, sunk in a deepish scrobicule, and are rather wide apart. The tubercles are with- 

 out order, but at the end of the anterior odd ambulacrum they assume a linear con- 

 vergent arrangement, and form a series of successive Vandykes, the angle being outwards 

 and forwards. The ambulacra are continued over the margin, a very small pore being 

 seen here and there. 



The ornamentation of the upper part of the test is very equal and small; it 

 becomes crowded at the margins, and at the under surface it gradually increases in the 

 dimensions of the tubercles and scrobicules, until the largest are found close to the 

 peristome. Beneath, the tubercles have a boss and mamelon and are perforate, and are 

 separated by minute granulations. 



The peristome is beneath the apical system, is longer than broad, elongate, longitudi- 

 nally narrow, pentagonal, and narrowest and angular anteriorly. It is deep, and the 

 floscelle is well developed. 



These buccal petals are broad, nearly closed, a tubercle often interposing between 

 the poriferous zones at their ends, wide apart ; and their poriferous zones are well 

 developed, and marked with grooves and costse. 



The poriferous zones have numerous pores in the outer row, and about half the 

 number in the inner row, connected by grooves which are rather wide apart. 



The inner pores are doubled in most instances ; and very frequently the innermost 

 series appear to be aborted and blind, possibly modified into sphseridia-pits. Two pores 

 are within the peristome. 



The anterior petal is usually the broadest, and is arched around by a small pitted 

 space whose pits are rather deep and small and irregularly placed. This space is con- 

 tinued forwards, and also extends sometimes on both flanks of the anterior petal. The 

 antero-lateral buccal petals are more pointed than the odd one, and are surrounded by 

 a row of large tubercles. 



The postero-lateral ambulacra also have a tubercle at their open distal end, and 

 posteriorly they are bounded by the commencement of the median pitted space, which, 

 reaches forwards to the posterior edge of the dense peristomial lip. The buccal petals 



l2 



