164 JACKSON AND JAGGAR — STUDIES OF MELONITES MVLTIPORVS. 



duced column more than one column out of 

 place to the left or right. The same remark 

 applies to all the studies of Palteechinoids as 

 presented in the succeeding paper, excepting the 

 case of Melonites septenarius (plate 9, figure 49), 

 ,Y as there described. 



The heptagonal plate adjoining the terminal 

 pentagon should by rule lie to the right of the 

 pentagon terminating odd-numbered columns, 

 ..X and to tlie left of the })entagon terminating 

 even-numbered columns. The position of the 

 hcjitagonal plate is shown in 171 cases, and of 

 those it occupies the correct position in 122 in- 

 stances and the incorrect position in 49 in- 

 stances. In other words, it occupies the correct 

 position in 71 per cent of the cases. 



From this close adherence to the theoretical 

 method of growth we are justified in giving the 

 annexed diagram as representing the correct 

 method of phite arrangement in Melonites and 

 the average number and relations of j)lates ex- 

 istent in Melonites multiporns in the adult con- 

 dition. In the figure all the ] elates are put in 

 according to rule as deduced from the compila- 

 tion of numerous critical observations. The sup- 

 posed initial plate I'is included in the figure so 

 as to indicate all the plates it had at any i)eriod 

 of growth, but it should be distinctly under- 

 stood that tliis plate is typically resorbed in the 

 adult condition. Nine columns of plates might 

 have been introduced in this figure, but it is 

 intended to represent the ideal, and 8 columns 

 are somewhat more frequent in perfect speci- 

 mens tlian 9. The lines A", F, Z are drawn so as 

 to bisect 8 columns of plates. They therefore 

 indicate by their progressively narrowing angle, 

 the stringing-out arrangement of plates in the 

 Figure i.-/Aa/ A,,a„^^,,nent ^Q^^r^] ^rca as dcscribcd ou page 150. (Com- 



oj intt'fatubiilacral Plates tn i o r« o 



Melonites tnuitiporns. parc with thc liuc .Y- }" iu pUitc 3, figurc 13.) 



H 



