DESCRIPTION OF MELONITES GIG ANTE US. 175 



were still existent. In the area figured all the plates were preserved 

 entire, excepting where vacancies are shown. 



At the ventral termination of the area, plate 5, figure 21, there is a row 

 of 3 plates. This area is also shown as area A in plate 4, figure 19. The 

 median plate 3 is hexagonal and is the initial plate of column 3, the 

 first formed column of median hexagons. Column 3 obviously originates 

 with one adambulacral column on either side, the universal position of 

 this column. Studying this first row, it is seen that on the ventral border 

 the median plate presents an angle ; the two lateral plates a comparatively 

 straight edge (plate 5, figure 22). This form of outline corresponds with 

 that seen in Melonites muUiporus at the ventral border of area E (plate 2, 

 figure 2). It consequently corresponds with the ventral termination of 

 the second row of that species, as shown in area A (plate 2, figure 2) ; 

 also the similar area of Oligoporus coreyi (plate 6, figure 25). From this 

 evidence it is unquestionable that the first row of plates, in the specimen 

 of Melonites giganteus, is absent from separation of the same after the death 

 of the individual. The same feature is seen at the base of 4 areas, A, C, 

 G and /, as shown in plate 4, figure 19 ; but area E is less perfect ven- 

 trally (see table, page 180). 



This first row of interambulacral plates could not be absent from re- 

 sorption during life by enlargement of the peristome in Melonites giganteus, 

 as discussed in Archseocidaris^ on page 215, because in that case the ventral 

 border would probably present a straight line, as in Melonites multiporus 

 (plate 2, figure 3). The two lateral plates, numbers ] and 2, at the ven- 

 tral border are therefore the second plates in their columns and form the 

 base of the two columns of adambulacral plates. In the reconstruction 

 of the base (plate 5, figure 22) the ventral plates of the two lateral columns 

 are shown at 1 and 2, as indicated by dotted lines, succeeded by plate 3 

 and its adjacent plates, which are the first plates shown in the specimen 

 (plate 5, figure 21). The angulated ventral face of this first row would in 

 itself indicate the absence of at least one row, but taken in conjunction 

 with the studies of the same areas in Melonites multiporus and Oligoporus 

 coreyi the evidence is incontrovertible. 



The fourth column is introduced in the next row above the third by 

 the terminal pentagon 4 (plate 5, figure 21). At its origin it has one 

 column on the left and two on the right, being thus one column too far 

 to the left by our law of alternation. In areas C, E, G and / (plate 4, 

 figure 19), however, it occupies its normal position, with two columns on 

 the left and one on the right. A similar variation is shown in Melonites 

 multiporus (area /, plate 2, figure 2). In 4 of the 5 areas in which this* 

 plate is shown in Melonites giganteus. it occupies the normal position, as 

 shown in the table, page 180. It is to be noted that this column 4 is the 



