1900.] 



MB. F. P. BEDFORD ON MALAYAN ECHINODEBMS. 



279 



unrepresented in tbe peristome of Eehinotliuridce), number in 

 adults normally 9 in one row and 8 in the other row of the pair, 

 although occasionally there may be 8 and 7 respectively. In 

 A. urens there are 9 in each row (according to the Sarasins), and 

 in A. grubei there are 12. The coronal plates, both amhulacral 

 and iuterambulacral, are like those described by M. de Loriol for 

 Amboina specimens of A, variwm, but the ambulacral edge of the 

 narrow interambulacral plates is devoid of tubercles. There are 

 three distinct kinds of pedicellariae. 



Stewart's organs are very well-developed and of the same 

 shape as in A. urens, and the muscular partitions are developed 

 to the same extent as in that form. 



The alimentary canal does not seem to have been described in 

 detail in any species of the genus, so that I do not know if the 

 condition occurring in this species in universal throughout the 

 genus, or whether it forms a " specific character " ; but in addition 

 to the two loops of the alimentary canal occurring in other 

 regular Echinoids (the adoral of the two being connected with the 

 siphon), it makes two additional loops within the former before 

 reaching the " siphonal intestinal loop," these additional loops 

 being situated round the top of the lantern of Aristotle (the 

 siphon appears to be absent). 



w.v. b.v. 



e.n. 



c.p. c.t 





^ 





!/■ 



Radius of Asthenosoma heteractis (transverse section). 



This section passes between the branches to the ambulacral pores, and is 

 thus slightly oblique. 



w.v. = radial water-vessel. 

 b.v. — radial blood-vessel ? 

 r.s. = radial sinus (pseudohsemal 

 canal). 

 *'. = septum between outer and 

 inner radial nerves. 

 e.n. — epineural canal. 



ms. = mesentery formed from the 

 endothelium of the body-wall. 



c.e. = endothelium lining body-wall. 



c.p. = calcareous plate (decalcified). 



c.t. = connective tissue. 

 i.r.n. = inner radial nerve (ganglion). 

 o.r.n.= outer radial nerve. 



Another character of some morphological interest which does 

 not Rpern to have bpen noticed by the Drs. Sarasin in A. urens, or 



19* 



