MELONECHINUS. 383 



species, but in its general characters would serve for any species of the family. Lines are 

 drawn through succeeding rows and numbered consecutively from one upward. It is seen that 

 every plate is accounted for and that the angle representing each row, as indicated by dotted 

 lines, deepens progressively passing dorsally. The row in which a given column makes its 

 appearance is indicated on the right side, and the number of the rows from the base or peri- 

 stomal border is seen in the left side of the diagram (p. 378). 



As column 1 is theoretically considered as arising in the primordial interambulacral plate 

 (text-figs. 22-31, p. 70), which has been resorbed, there is no number to represent the row in 

 which it originates on the right side of text-fig. 246. In this choice specimen the introduction of 

 the earlier columns as added can be readily seen in the photographic figure (Plate 55, fig. 1), 

 but they are all plainly seen in Plate 57, fig. 1, and text-figs. 245, 246. In the basicoronal row 

 the two plates are in place in areas G and I, and one of the two is in place in areas A and C. 

 In area E these two plates are restored as indicated by dotted lines. In the second row there 

 are three plates in all areas, the initial plate of column 3 being hexagonal as usual. In the third 

 row there are four plates in each area, the initial plate of column 4 being a pentagon. This 

 pentagon lies on the right of the center in areas A, E, and I, but on the left of the center 

 in C and (_}. The initial plates of columns 5 to 8 (with the exception of the initial plate of 

 column 8 in area C), are all pentagonal with a heptagonal plate either on the left or on the 

 right ventral border of the same. Column 5 originates in the center, in areas A and G in the 

 sixth row with a heptagon on the right or left ; in area C it originates on the left of the center 

 (unusual for odd-numbered columns) in the sixth row with a heptagon on the right, and in 

 ai'eas E and I, column 5 originates in the center, in the seventh row with a heptagon on the 

 right. Column 6 in areas A and E originates in the tenth row on the left of the center with a 

 heptagon on the left; but in area C it originates in the ninth row on the left of the center with 

 a heptagon on the right. In areas G and I the sixth column originates in the tenth row with 

 a heptagon on the right in G and on the left in I. C'olumn 7 originates in the center in all 

 areas, as is typical of odd-numbered columns. In areas A and C this column originates in the 

 thirteenth row with a heptagon on the left. In area E column 7 originates in the fifteenth 

 row with a heptagon on the right, and in areas G and I it originates in the fourteenth row 

 with a heptagon on the left in G, and on the right in I. Column 8 originates in area A 

 on the left of the center in the seventeenth row with a heptagon on the right; in area C col- 

 umn 8 originates on the left of the center in a tetragonal plate in the eighteenth row with a 

 heptagon on the right, also another heptagon on the left ventral border. In area E column 8 

 originates on the left of the center in the twenty-first row with a heptagon on the left. In 

 area G it originates also on the left of the center, but in the nineteenth row, with a heptagon 

 on the left. Finally, in area I, column 8 originates in the eighteenth row on the right of the 

 center with a heptagon on the left. 



