OF WESTERN SIND. 193 



Genus HEMIASTEE, Desor, 1847. 



(See anted,, p. 78, Part ii.) 



1. Hemiastee apicalis, Duncan & 8laden. Plate XXXIV, Figs. 1-7. 



Test of large size, marginal contour irregularly suboval, widely expanded laterally, 

 the greatest breadth lying across the posterior third. In front of this prominent lateral 

 protuberance the test contracts rather rapidly, passing sharply round the subcarinate 

 tumidity of the anterior interradial areas, and indented in front by a distinct but not 

 yery deep anteal sulcus. Behind the line of greatest breadth the outline of the test 

 contracts rapidly, giving a somewhat pointed appearance posteriorly. The length of 

 the test is slightly greater than the breadth, the proportions being as 1 : 0'923. The 

 greatest height of the test lies a little behind the centre, and is proportional to the 

 length as 0-56 : 1. 



The apical disk, which is small, is excentric in front, the anterior portion of the 

 median line being little more than one half of the posterior part. Seen in longitudinal 

 profile, the anterior slope shows only a slight convexity, the anterior extremity being 

 thick and tumid. The posterior slope of the test, after a short convexity along the 

 saddle-backed keel of the posterior interradium, descends with an almost precipitous 

 slope, the posterior margin being much less rounded than the anterior. Seen in trans- 

 verse profile, the test, when viewed in front, has a high and somewhat conical appear- 

 ance, the carinate portions of the paired interradia being distinctly visible. Owing to 

 the anterior declivity of the test, the postero-lateral keels and the posterior wall of the 

 antero-lateral petals are seen above the antero-lateral keels, and the prominent, well- 

 rounded keel of the odd posterior interradium attains midway a still greater elevation. 

 When seen from behind, the lateral portions of the dorsal profile have a fuller and more 

 tumid appearance than when seen from the front, and the general contour of the pro- 

 file is more convex, the median posterior keel being high and prominent. The position 

 of the periproct is high, and appears to have been situated at the commencement 

 of the inferior third of the height ; but accurate observation on this point is impos- 

 sible in the specimen under description, in consequence of fracture and imperfect 

 preservation. 



The apical disk is excentric in front and comparatively small. There are four 

 generative pores, the posterior pair being very wide apart ; and the posterior ocular 

 plates are widely separated and pushed asunder, as it were, by a remarkably broad 

 expansion of the central madreporiform body. 



The odd anterior ambulacrum is in a well-defined, rather deep groove, which 

 expands and becomes shallower as it approaches the margin, where it forms, however, a 

 conspicuous indentation in the anterior contour. It is continued, although greatly 

 diminished in depth, over the margin, and dies out just before reaching the peristome. 

 The pairs of pores, which are situated in small oval cavities, are placed obliquely, and 

 the pores of a pair are separated by a small tubercle. Near the apical extremity of the 

 ambulacrum the pores are very small and closely placed, but as they proceed outward 



