REMARKS ON TABLES OF PLATE ARRANGEMENT. 161 



area / terminates in a ventral plate, which is tetragonal or rhombic in 

 form. This plate, which is shown in plate 2, figure 6, is quite near the 

 dorsal termination of the area. 



Specimen number 3019 (page 169) shows only one area, which has 9 

 columns of plates. The ninth originates quite close to the dorsal termi- 

 nation of the area, as in the above case, and its terminal plate is rhombic 

 in form. The arrangement of the areas is entirely normal, excepting the 

 tetragonal plate and one heptagon, which is out of place. 



Specimen number 3020 (page 169) is normal throughout, except that 

 one column, the eighth, originated one column too far to the left; also 

 one heptagonal plate is out of place. 



Specimen number 3022 is entirely ideal in its arrangement through- 

 out, unusually normal in fact, for some variation is commonly met with. 



Specimen number 2992 (page 170) is peculiar in having one odd-num- 

 bered column, the seventh in area (7, one column too far to the right; also 

 two even columns in area A are too far to the left, and three heptagons are 

 out of place. One area, C, has but 7 columns of plates, Avhereas the other 

 has 8, both areas being complete dorsally. 



Specimen 2999 (page 170) has 9 columns of plates and is normal 

 throughout in its plate arrangement. 



Specimen 3004 (page 170) has two columns and' one heptagon out of 

 place. The irregular position of column 7 is noteworthy, because it is 

 unusual for odd columns to be otherwise than median in position. 



Specimen number 3006 (page 170) is entirely normal throughout. 



Having stated the law of growth in the interambulacrum of Melonites 

 multiporus, and having figured and tabulated the arrangement in many 

 specimens, it is desirable to foot up the results of the observations and 

 see how closely actual observations come to the assumed law of intro- 

 duction and arrangement of plates. In this summary are included all 

 the figures given of Melonites multiporus in the accompanying plates ; also 

 the tabulations of the same species. In a few cases the same area is in- 

 cluded in a figure and also in a table, when of course but one count is 

 made. For most of the details considered we have also included the 

 results obtained from the tabulation of Melonites giganteus, Jackson, as 

 described in the succeeding paper. From the context it will be made 

 plain when both species or only one species are included. " 



In considering this summary constant comparisons with the figures 

 of Melonites should be made, especially the ideal diagram on page 164. 

 Comparison is also requested with the plate arrangement illustrated in 

 the succeeding paper in the genera Oligoporus, Palceechinus, Archseocldaris, 

 Lepidocidaris and Lepidechinus, where the same method of growth pre- 



