OF WESTERN SIND. 145 



than the breadth, regularly rounded in front, and contracting along the sides towards 

 the posterior extremity, where a faint trace of rostration is produced. The height is 

 less than one half the breadth, and is proportional to the length as 0'33 : 1. The dorsal 

 surface is regularly convex, and the margins are not particularly thick or tumid, the 

 curvature of the dorsal area being more arched and continuing nearer to the ambitus 

 than in A. subrotundus. In the longitudinal profile of the test the posterior and the 

 anterior slopes are nearly equal in curvature, the latter, however, being slightly more 

 tumid. The transverse profile shows a regular and well-developed convexity, merging 

 into the comparatively thin, rounded margin. The actinal surface is almost flat, and 

 has nothing of the pulvinate character usual in the species of this genus, the flatness 

 terminating with only a comparatively slight and abrupt rounding at the extreme margin. 

 There is a slight depression towards the peristome, but unfortunately that portion of 

 the test and its immediate neighbourhood is concealed by a mass of matrix. 



The apical disk is slightly excentric in front ; but nothing can be said about its 

 structure, owing to the destruction and obliteration of this part in both the specimens 

 we possess. Indeed the whole of the abactinal area is in such a bad state of preserva- 

 tion that only the general features can be indicated. 



The ambulacra are flush with the surface of the test, and the poriferous zones 

 contract somewhat rapidly after attaining the maximum width, the petaloid portion thus 

 appearing to terminate a little before the margin is reached. The outer line of the 

 posterior poriferous zone in both pairs of petals is somewhat more curved than the com- 

 panion zone ; and in the posterior ambulacra the whole petal is slightly bent forwards 

 (i. e. away from the posterior extremity) before passing over the margin, the curve being 

 very marked when the interporiferous area is examined independently. The posterior 

 pair of petals are rather widei: than the anterior petals. The widest part of the pori- 

 ferous zone is situated rather nearer the outer than the apical extremity of the petal, and 

 at this point the poriferous zone is ^g- of the width of the interporiferous area, and 

 thence the decrease in the width of the zone takes place rather rapidly. The greatest 

 width of the petal is situated a little nearer the extremity of the petal than the point 

 of greatest poriferous width. The widest part of the interporiferous area is at the 

 margin, where it is slightly greater than twice the width of the poriferous zone at its 

 widest part. 



The ornamentation of the dorsal surface is almost entirely destroyed ; and the 

 traces that remain are so faint that it is impossible to' make any useful observations in 

 this direction. On the actinal surface the primary tubercles are smaller and more 

 widely spaced than in A. subrotundus, and are surrounded by simple rings of miliary 

 granules, which appear to stand somewhat isolated and distinct, in consequence of the 

 intermediate spaces being unoccupied by granules. 



The whole of the peristome and a portion of the periproct are concealed by matrix. 

 The periproct is elongate and pyriform, the aboral margin being well rounded. The 

 aperture is 14 millim. long and 7"5 millim. broad, and its aboral extremity is not more 

 than 5 to 6 millim. distant from the extreme margin. 



Bemarks. This species is distinguished from its Indian congeners by the flatness of 



