20 FAUNA OE BALUCHISTAN. 



become more rounded, but the upper surface is much more inflated, the test has 

 become more globular, and the profile forms nearly a complete ellipse. 



In the third variety, var. glohoaa, the pentagonal shape has almost disappeare d 

 and the test has become nearly circular; at the same time, the inflation of the upper 

 surface has gone still further, the profile forming an ellipse nearly approaching 

 a circle, the test thus becoming globular. 



As may be expected from this description, the lower surface of var. penta. 

 gonalia is large, flat, and only slightly pulvinated near the circumference; in the 

 var. tumida it is a little more inflated and in the var. globosa it is nearly as much 

 inflated as the upper surface. Ambitus rounded in a varying degree, 



Apical disc central, very small composed of flve genital plates, four of which 

 are perforated by large holes ; the fifth imperforate, and flve small ocular plates 

 perforated by tiny holes ; the two posterior ones nearly overlap the imperforate 

 genital plate; madreporiform plate a little larger than the other genital plates. 



Ambulacral areas narrowly lanceolate, extending from the apical disc to the 

 mouth ; the poriferous zones are linear, slightly concave ; the pores are minute and 

 placed in oblique pairs ; in passing around the ambitus and on the lower surface the 

 pairs arrange themselves in numbers of three, in oblique lines. 



The peristome is out of the centre, just a little nearer to the anterior margin ; 

 it forms an irregular pentagon with its long axis obliquely directed from right to 

 left. Periproct large, longitudinal and pyriform, just above the posterior margin 

 but invisible from above ; from below only its lower edge can be seen ; in yar. penta- 

 gonalis the periproct is hardly above the margin, while in var. globosa it seems to 

 be right in the middle of the height of the test. 



The ornamentation consists of small imperforate tubercles which are deeply 

 sunk in a very narrow scrobicule; on the lower surface the tubercles are larger and 

 more numerous than on the upper surface, where they are smaller and more spar- 

 ingly distributed, with numerous delicate granules between them. On the inter- 

 poriferous zone of the ambulacral area the tubercles show a tendency to arrange 

 themselves into rows, of which there are eight altogether ; the three outer ones are 

 very regular, and their tubercles, increasing in size towards the interior, are arranged 

 in alternating lines ; the two inner rows are less regular. On the interambulacral 

 areas the tubercles are irregularly distributed, but apparently they are more crowded 

 towards the lower lines than in the interior. 



LocalUy and stratigraphical position. — Des Valley, horizons 2 and 4, very 

 common ; rare at Mazar Drik, horizon 8. 



Memarks. — It might be more advisable to describe the above three varieties 

 under three separate specific names, as they are seemingly well characterised by the 

 differences in the shape of the test, than to unite them under one common name. 

 I fully admit that if we take, say, fig. I of var. pentagonalis SiU^ ^^. 5 of var. 

 globosa, this view would be justified, provided we had only these two specimens and 

 no intermediate links ; but these two extremes are so intimately connected by 

 imperceptibly varying links, that it is impossible to consider them as separate 

 species when we have proof that they only form the terminal points of a continuous 



