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 i- .-.-.-M 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 make- it- 

 appearance is indicated on the right side, and the number of the rows from the ba.-e 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 iiiterambulucral 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. 24(>. In this choice specimen t he int roduct ion 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 ami < . 

 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 G. 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 cither 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 

 areas 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. Column 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 ar- 

 ea 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. 



