926 W. KEEPING ON THE GENUS PELANECHINUS. 



Every one of these plates that is well exposed shows a pair of pores 

 situated somewhat out of its centre, and surrounded by an oval ring. 

 They are arranged roughly as a single series running from the mouth- 

 opening in a line with the poriferous zones of the corona; but there 

 is no marked difference in character except the presence of the pores 

 themselves to define a poriferous and a non-poriferous zone upon 

 this part of the test. If there are any plates here without pores, to 

 correspond with the proper interambulacral areas of the corona, 

 these must be small, and they may perhaps be absent. 



The primary tubercles of this species (fig. 7) are proportionately 

 small when compared with the size of the test. They are deeply 

 perforated, and are elevated upon prominent bosses, which are ex- 

 panding at the base, and smooth (uncrenulated) at the summit. 

 The surrounding areolas are wide, extending almost to the upper 

 and lower edges of the plate, thus leaving room only for a row of 

 small granules between themselves and the border. Contiguous 

 areolas are sometimes well separated by a broad miliary space ; more 

 usually they are marked off only by a narrow line of granules and 

 minute tubercles ; and in some places they are actually confluent. 



The secondary tubercles differ from the primary ones only in size 

 and in their proportionately smaller boss. 



According as the space between the primary tubercles is greater 

 or less, so we have usually secondary tubercles, minute tubercles, or 

 only granules upon it. The tubercles of the ambulacral and inter- 

 ambulacral areas are in no way themselves distinguishable ; and 

 those upon the scale-plates of the mouth-area differ from them only 

 in size. 



The two orders of spines are seen strewed over the whole test. 

 The primary ones (fig. 8) are small and slender, and, with the 

 pocket-lens, are seen to be longitudinally suloated. The head is long 

 and slightly swollen, with a faint ring surrounding the glenoid cavity ; 

 its collar is prominent and crenulated by broad and deep incisions, 

 which, gradually narrowing along the steep neck, become continuous 

 with the sulcations of the stem. This stem is very uniform, tapering 

 but slightly, and it is hollow. 



The secondary spines vary from -J- inch to about \ inch in length. 

 They are* slender, taper very slightly, and end in a blunt point. 

 Their articular end is much less conspicuous than in the primary 

 spines. Other spines intermediate between these two were supported 

 by the secondary tubercles. 



Measurements* 



millim. 



Diameter of test 100 



„ ,, actinal area 34 



Breadth of interambulacral area at oral extremity . . 13 



,, „ „ „ equator 44 



„ ,, „ plate at oral extremity . 6 



Height of interambulacral plate at oral extremity. . 2 



Breadth of interambulacral plate at equator ...... 23 



