OF WESTERN SIND. 91 



lacrum are separated by a slight, flat, low ridge, which is narrow close to the apical 

 system, and enlarges to the ambitus. The ornamentation of this wedge-shaped, trian- 

 gular, and slightly elevated ridge is smaller than that of the interradials on either side. 

 On its flanks and looking upwards and outwards are the pairs of pores of each pori- 

 ferous series. They are very small, oblique, and in slight hollows ; a minute tubercle 

 intervenes between the pores of each pair, whilst the pairs are separated by a ring of 

 miliaries. 



The pores cease before the position of the fasciole is attained ; and a few are visible 

 close to the mouth. 



The anterior lateral ambulacra are long, slender, narrow, crooked, nearly flush with 

 the test (so slight is their groove), open at the end, and nearly transverse (so great is their 

 open angle). Each ambulacrum has a decided curvature, the concavity being directed 

 forwards in the outer half, and posteriorly near the apical system. 



The interporiferous space is very narrow ; and the posterior poriferous zone is slightly 

 larger than the anterior. The pores in the anterior poriferous zones are smaller than 

 those of the posterior, are very slightly elongate in outline ; those of the posterior zone 

 are unequal in size ; the row nearest the interporiferous zone consists of smaller and 

 circular or faintly oval or elliptical pores, whilst the posterior row contains larger 

 pores which are elongate ellipses. The pores are conjugate and well separated ; the 

 cross-banding has a row of miliaries on it. There are about 26 pairs of pores, and 

 those nearest the apical system are very small in proportion to the others. 



The posterior ambulacra, slightly shorter than the antero-lateral, form an acute 

 angle with each other, are in a slight groove, which is much more decided than that 

 of the others, are closed at the end, where they are in contact with a fasciole, 

 and are straight. Narrower than the anterior lateral, the posterior ambulacra have 

 smaller pores, which are circular, oval, and elongate in outline. At the peristome 

 the lateral and posterior ambulacra are represented by large wide-apart pores, and they 

 crowd out the posterior lateral interradial areas 1 and 4 from the margin of the 

 peristome. 



The anterior interradials are rounded off; and there is a faint elevation in the 

 angle formed by the ambulacra at the apical system ; a rounded low keel is on the 

 lateral interradials ; and the posterior one has a convex surface above, which is narrowed 

 near the apical system. Posteriorly, the odd interradial slopes slightly to the rear, and 

 then is truncated, its direction being nearly vertical ; but there is a slope backwards to 

 the margin. This part is broad, has a very faint vertical groove below the periproct ; 

 and this is large, widely open, and nearly circular or elongate in outline. 



Actinally, the interradials are convex, and the posterior has a well-developed plas- 

 tron between the long narrow anterior ambulacra. It has a broad low central keel 

 reaching from theposterior projecting point forwards to the mouth, where it reaches down- 

 wards slightly, and forms the base of the hind lip. The plastron has an ornamentation 

 of very regular hexagonal spaces, bounded by raised margins (the united scrobicular 

 raised edges), environing a flat areola, on which, nearest one end, is a boss and mamelon, 

 which is faintly perforate and crenulate. 



