THE TWENTY-RAYED STARFISH. 203 



ble to conclude this paper, although in an abridged form. 



Investigators do not agree in regard to the position of the madre- 

 poric plate in Asteroidea. Ludwig ('99), dealing with the genus 

 Astcrias, says : 



' Falls wie es, trotz der nicht seltenen Ausnahmen die Regel ist, 

 nur eine einzige Madreporenplatte vorhanden ist, liegt sie stets im 

 vorderen linken interradius, wenn man den Seesterne bei abwarts 

 gerichtetem Munde mit dem Interradius des Afters nach vorn 

 stellt," p. 540. 



FIG. i. A copy of Ludwig's figure of the asteroid groundplan, showing 

 Ludwig's morphological "anterior" end. (P. 537.) 



A, anus; h.R, posterior radius; l.h.I, left posterior interradius; l.h.R, left 

 posterior radius ; I.i'.I , left anterior interradius ; l.v.R, left anterior radius ; M.P, 

 madreporic plate : r.h.I , right posterior interraditis : r.h.R, right posterior 

 radius ; r.v.I , right anterior interradius ; r.v.R, right anterior radius ; r.7, 

 anterior interradius. 



Agassiz ('77) claims that the madreporite is always in the suture 

 of the terminal arm of the pentagon, which brings it opposite the 

 third arm. This is also the view of Bury ('95). Rathbun ('87) 

 says it is generally placed about midway between the center and 

 the margin of the disk, and Sedgwick ('09) records that the 

 madreporite varies in number in various species of starfish. 



Delage and Herouard ('03) say: " Elle est situee dans la region 

 apicale, tout pres de la centro-dorsale, clans un interradius autre que 

 celui qui porte 1'anus. Le madreporite determine nne deuxieme 

 symetrie bilaterale, mais qui est alteree par 1'anus, comme celle 



