OF WESTERN SIND. 315 



at the ambitus, and consequently four of the pairs of pores belonging to the outer 

 vertical series. 



The interradial plates are broad but short, the breadth at the ambitus being rather 

 more than four times the length {i. e. depth), the actual dimensions being 21-5 millim, 

 and 4-75-5-0 millim. respectively. Each plate bears a horizontal line of uniform and 

 widely-spaced primary tubercles, very slightly larger than those on the ambulacral 

 areas. In the neighbourhood of the ambitus there are four tubercles in this horizontal 

 line, the position of which upon the plate is rather below the middle. At the end of 

 the plate adjacent to the poriferous zone an additional primary tubercle, of equal size 

 to those described, stands near the aboral corner of the plate, and there are thus five 

 primary tubercles on each plate at the ambitus ; this additional upper tubercle, how- 

 ever, is not found on more than five or six plates above the ambitus, and on the upper 

 ones even of these becomes reduced in size to a small secondary. The first tubercle of 

 the true horizontal series (next the poriferous zone) does not extend beyond two 

 thirds of the distance between the ambitus and the apex, and it is the second tubercle 

 only whose series extends from the peristome to the apex, this tubercle being the sole 

 occupant of the five or six upper plates of the interradial area ; the third tubercle 

 extends about as far as the first above mentioned, but appears to maintain its size 

 better, the tubercles of the first series diminishing rapidly as they approach their upper 

 limit. The fourth or innermost tubercle does not extend much beyond halfway 

 between the ambitus and the apex. Consequent on this disposition of the tubercles, 

 there is a median naked and slightly depressed or trough-like area in the uppermost 

 • region of the interradia. A number of widely-spaced miliary tubercles are present 

 on the plates, and a more or less definite horizontal series occurs along the aboral 

 margin of the plates, at least near the ambitus and a little below. 



The peristome is tolerably wide, decagonal, impressed, with the actinal surface 

 swelling tumidly between the peristome and the margin of the test ; and the diameter 

 is a little more than one fourth that of the test (23 millim. in a specimen whose 

 diameter is 80 millim.). The mouth-slits are deeply cut, and extend as far as the 

 level of the fourth tubercle in the ambulacral area. The notches are narrow and have 

 a conspicuous raised rim, most prominent on the interradial side, where there is also a 

 considerable thickening near the upper third of the length ; this causes the notch to 

 have a slightly curved appearance, as if bending towards the interradium. On its 

 embouchure into the peristome the notch expands rather rapidly, its interradial side 

 being more cut away than the ambulacral. The peristomial mirgin of the ambulacral 

 areas is nearly straight, very faintly indented at the median line, and is nearly twice as 

 broad as the interradia. 



The apical disk is not preserved in any of our specimens. 



Young form. A small test, 56 millim. in diameter and 40 millim. in height 

 (slightly crushed), presents all the characters of the adult form in the structure of its 

 ambulacral areas, and is unmistakable. The specimen unfortunately is so badly 

 preserved and so much destroyed by weather-action, that it is quite unfitted for 

 description, 



2u2 



