138 THE FOSSIL ECHINOIDEA 



are round, the pairs slightly oblique, and the conjugation scarcely perceptible. The 

 pores of a pair are wider apart at the inner third of the zone and approximate gradually 

 as they proceed outward, and rapidly towards the apex — a structure which emphasizes 

 the marked and graceful petaloid curve of the zones. There are about twelve pairs of 

 pores in each zone. The interporiferous area of the petal is sublanceolate in outline and 

 very broad, equal in width to more than twice that of the poriferous zone at the widest 

 part. The interporiferous area within the petal is costulate or tumid — a feature usually 

 more marked in the posterior pair of petals than in the other three. The posterior 

 petals are more disticntly petaloid in outline, in consequence of the poriferous zones 

 visibly curving inward and reducing the breadth of the interporiferous area towards the 

 extremity of the petal. In the three anterior petals the inner series of pores, after 

 attaining the place of the greatest breadth of the petal, form an almost straight line, and 

 the interporiferous area is consequently little, if at all, contracted towards the outward 

 extremity of the petal. The anterior odd petal is slightly smaller than the others. 



There are no large pores in continuation of the petal-series visible on the actindi 

 surface, but in their place a very great number of minute and closely crowded foramina 

 occupy the whole of the horizontal sutures between the ambulacral plates and also the 

 vertical sutures along the line of junction of the ambulacral and interambulacral plates, 

 the horizontal series being much more crowded and numerous close to the peristome. 



The peristome is central, subdecagonal, and with the margin bevelled inward. The 

 pair of buccal or peristomial pores which open into the peristomial margin of each 

 ambulacrum are conspicuous but closely placed ; and there is a slight, tubercular, roof- 

 like development over each pair. The periproct is circular, nearly two thirds the 

 diameter of the peristome, and is situated nearer to the margin than midway between 

 the peristome and the posterior extremity. The tuberculation of the test is minute, 

 sunken in deep scrobicules, and rather widely spaced. 



Variations. Considerable variation occurs within certain limits in the shape of the 

 marginal outline of the test ; and these changes of form are found to be altogether 

 irrespective of size or age when a large series of specimens is examined, such as that 

 furnished by the present collection. The contour may assume almost any form between 

 an elongate ovoid, similar to that usually presented by the small existing species of 

 Echinocyamus {E. pusillus), and the ovoid pentagonal test characteristic of such living 

 urchins as Clypeaster subdepressus. 



Memarks. This species presents some alliance to Sismondia Scemanni, de Loriol, 

 from the Nummulitic of Egypt, but appears to differ in the more pentagonal outline, 

 the more inflated margin, the wider and more open petals, and probably also in the 

 character of the costulation of the interporiferous areas. 



A variety, var. siLfflata, nobis, occurs in the Nummulitic of Kachh. 



Dimensions. The largest specimen measures 11 millim. in length, 10 millim. in 

 breadth, and about 3 millim. in height. 



Others measure lO'D millim. long, 9-00 millim. broad, and about 2-75 high. 

 9-3 „ 8-25 „ „ 3-00 „ 



7-0 „ 5-50 „ „ 2-00 „ 



