OF WESTERN SIND. 181 



lated, and the portions corresponding to the ambulacra are comparatively narrow strips. 

 On the raised peristomial rim there is a small, feebly developed granule on the ambu- 

 lacral portion of the rim at its junction with the apparently continuous interambulacral 

 portion; there are thus two granules near together opposite each ambulacral area. 

 These granules, however, are not always clearly discernible in every specimen and are 

 not always equally developed in each individual. Outside the peristomial ring the 

 poriferous zones of the ambulacra are represented by three or four pores closely placed 

 in uniserial line, and there is no tendency to form a phyllode. 



The periproct is elongately oval or elliptical, placed longitudinally at the upper 

 part of the vertical posterior truncation of the test ; its length is twice its breadth, and 

 is about equal to the transverse diameter of the peristome. Above the periproct the 

 odd posterior interradium forms a slightly tumid keel along the outer portion of the 

 median dorsal line, but no roof whatever is formed over the aperture ; and when viewed 

 abactinally from behind, the sides of the test seem to be nipped-in at the sides of the peri- 

 proct, which causes this aperture to appear to be placed at the extremity of a somewhat 

 pointed prolongation of the test. Beneath the periproct there is no channel, although 

 a very faint median depression laay sometimes be noticed ; and the inferior margin of 

 the posterior truncation is full, tumid and abruptly rounded, joining the prominent 

 median tumidity of the actinal portion of the odd posterior interradium. 



Variations. The chief variations noticed in this species are those which affect the 

 marginal contour, the relations of length to breadth, the position of the apical summit 

 of the test, and the consequent modification in the longitudinal profile. These points 

 have been referred to above, and the other details of structure appear to be very con- 

 stant. An elongate variety, produced and contracted posteriorly, and with the apical 

 summit excentric behind, is shown in Figs. 15 and 16 ; and a small subrotund variety, 

 which appears to be uncommon, with the apical summit corresponding with the apical 

 disk, is given in Figs. 17 and 18. 



Bemarks. Although the Indian species does not show the peculiar characters of 

 the peristome in such a marked manner as the type form of the genus, I. Beggiatoi, 

 Laube, sp., we do not hesitate to include the present Echinoids in the same category. 

 The two species are well distinguished from other EchinantUnoB and cannot be 

 mistaken. 



Bimensions. 



a. h. c. d. 



millim. milliin. millim. millim. 



Length of the test 27 29 22 18-6 



Breadth of the test 23 23-5 20 16 



Height of the test 17 17-5 13 13 



Localities. In the Khirthar series of strata:— i. Baili, west of T6ng. Survey- 



n G304 



number ^g— 



ii. Trak! hilLfseventeen miles south of Blila Khdn's Thana. Survey-number 



-gs-. (A small example.) 



2b 



