DESCRIPTION OF MELON ITES GIGANTEUS. 



181 



Table of Plate Arrangement of Melonites giganteus, sp. nov. — Continue|^ 



Melonites giganteus^ sp. nov. 



Ambulacrum H. 



Interambulacrum I f. 



Ambulacrum J. 



^fl 





>. 



a 



o 



cS 



"S 



















cS 



'*-! 



o 



o 



E 





_2 



> 





-'^ 





0) 



a 



01 



o 



=4-1 



.^d 



s 





.a (» 



fl M 



r. bC 





5 





1-^ 







cs 



C 



cS 



a 



c 



.Q 



s 



s 



o 



S 



S 



s 



s 



bC 





3 

















o 



0) 



*-l 



o 



o 



^ 



o 



H 



o 



O 



o 















Heptagon on left or right 

 of terminal pentagon. 



Four columns of plates at base. 



11 



11 



P 



25 



5 



10 



P 



20 



5 



- n 



P 



17 



4 



8 



P 



14 



3 



7 



P 



1(» 



3 



6 



P 



8 



2 



5 



P 



5 



2 



4 



P 



3 



2 



3 



X 



2 



1 



Right.* 



Left. 



Right. 



Left. 



Right. 



Bight. 



Indistinct. 



Truncates initial plate 3. 



First row of plates wanting. 



Four columns of plates at base. 



In the interambulacrum A (plate 5, figure 21), in column 1, from the 

 ventral to the dorsal end, as far as preserved, 29 plates may be counted ; 

 in column 2, there are 31 plates. If column 1 were as perfect dorsally as 

 column 2 there would without doubt be 34 plates also. Column 3 has 

 35 plates, column 4 has 33 plates, column 5 has 33 plates, column 6 has 

 30 plates, column 7 has 28 plates, column 8 has 25 plates, column 9 has 

 23 plates, column 10 has 19 plates, and column 11 has 12 plates. Add- 

 ing these, there are seen to be 301 plates existent in the interambulacrum 

 (plate 5, figure 21), or, adding the 9 plates wanting in the first column, 

 310 plates in all. Supposing the other 4 areas to have approximately 

 the same number, as is the fact, then the interambulacral plates of this 

 specimen are no less than 1,550 in number, to which may be added the 

 two ventralmost plates wanting in each area and a few dorsal plates not 

 preserved clearly enough to be made out. 



It is believed that the columns of ambulacral and interambulacral 

 plates as introduced represent stages in growth, as discussed in the sec- 

 tion " General Results and their Bearing." Assuming this to be correct, 

 then Melonites giganteus when young had 4 columns of ambulacral plates , 



* But not in next column. Compare with heptagon H, associated with pentagoa 8, of plate 2, 

 figure 7. 



t Interambulacral complete at dorsal portion of area. 



t Terminates with accessory heptagons and tetragonal plate, as shown at this area in plate 5, 

 figure 21, and plate 4, figure 19. There is no similar peculiarity about pentagon 9 in area G. 



