346 POURTALESIA MIRANDA. 



following very nearly the edge of the deep anterior groove in which the odd 

 anterior ambulacrum (PL XVIII. /'. ;) is placed. 



The odd ambulacrum is made up of two lines of pores far apart (PL XVIII. 

 f.S). The abaetinal system, consisting of four large genital openings (PL 

 XVIII f. 0) placed close together, with the madreporic body tolerably well 

 defined in the centre, is situated at the origin of the anterior groove ; this is 

 flanked by prominent ridges extending from the apical system, gradually dis- 

 appearing towards the mouth, placed at the outer extremity of the anterior 

 groove (PL XVIII. f. ,',); this increases in depth on the lower surface (PL 

 XVIII. f. S), resembling in fact the anal groove of Echinobrissus, and allied 

 genera, in an inverted position. The actinal system is elliptical, the long axis 

 in the trend of the groove very large, with sharply defined edges covered by 

 very minute plates (PL XVIII. f. 8). There are no indications of a floscelle. 

 The odd ambulacrum carries large, thick tentacles, with rounded extremity, 

 moderately close together (PL XVIII f. 1!)) ; while the tentacles of the other 

 ambulacra are placed, one for each plate, far apart, so as to readily escape 

 notice, isolated as they are in the midst of the prominent and peculiar pedicel- 

 larirc which are so abundant, especially along the line of the posterior ambu- 

 lacra. These pedicellariaj consist of a stem upon which articulate three slen- 

 der, contractile arms (PL XVIII. f. 1U, 17, IS), each terminating in a disk, 

 with milled edges.* There is no petaloid portion in the ambulacra ; they 

 are all composed of simple pores from the mouth to the apical system. The 

 spines are long, curved at the base, as in Spatangoids (PL XVIII. f. 10); 

 the tubercles to which they are attached have a smooth scrobicular area. The 

 mammary boss is small, crenulated, perforate in old, imperforate in younger 

 tubercles, surrounded by a large granulated scrobicular area (PL XV J 1 1 . 

 /'. //), and raised above the surface of the test, to which the milled ring is 

 attached by a very flexible muscular membrane (PL XVIII. f. l .', 13). 

 There are smaller spines of a similar structure, somewhat more fan-shaped 

 (PL XVIII. f. lJ t ); scattered irregularly over the test, but quite distant. 

 The whole appearance of the test is bare, the primary tubercles carrying 

 long spines being placed far apart in the lateral posterior interambulacral 

 areas (PL XVIII. f. l) ; and it is only on the ridges along the anterior 

 groove, round the mouth and anus, that the small spatulate spines (PL XVIII. 

 f. 14) are closely packed together. 



* By an oversight, the description of these pedicellariae, in the Preliminary Report, became connected 

 with that of the tentacles. 



