The Pluteus of Laganum sp. 



133 



15 



FIGS. 4 to 15. Series showing development of plates and spines of the permanent skeleton of 

 Laganum. Figs. 4, 5, 12 to 15 viewed from ventral surface. 6 to 11, from dorsal surface. 

 b 1 , 6 2 , 6 3 , branches from each of the six primary rays, which by uniting with one another and 

 with the wheel-like structure at their exterior ends, form 6 radiating plates in the base of the 

 spines; c, 6 branches of the primary rods which form the cup-like basal portion of the spine; 

 p, plate; ps, portion forming small secondary plate which lies between the primary one and 

 the spine; w, portion forming wheel-like base of the spine. Figs. 4-10, X466. Figs. 13-15, 

 X350. 



FIG. 16. Permanent plates and spines viewed from the oral surface, showing their characteristic 

 arrangement around the anlage of the adult mouth, m. a. p., adult plate; a.s., adult spine. 

 X265. 



