MELOXECHINUS. 389 



higher and laterally fan-shaped; also pore-pairs lie near the inner border of demi-plates and 

 the middle of isolated plates (Plate 61, fig. 4) instead of near the outer border of each plate 

 as on the exterior (compare Plate 56, fig. 5). 



The interambulacra are about equal in width to the ambulacra, and for the most part 

 are preserved as molds of the interior; a few plates, however, are in place at various parts of 

 the test. There are eight columns of plates at the mid-zone and nine further dorsally in each 

 of the five areas. An area drawn mostly from the internal mold is given in Plate 61, fig. 2. 

 The basicoronal plates are restored, as indicated by clotted lines. There are three plates in 

 the second row and four in the third as usual. Column 5 originates in a pentagonal plate 

 in the middle of the area in the seventh row and bears a heptagon on its right ventral border. 

 Column 6 originates in a pentagon on the left of the center in the tenth row and bears a heptagon 

 on its left ventral border. Column 7 originates in a pentagon in the middle in the fourteenth 

 row with a heptagon on its left ventral border. Column 8 originates in a pentagon in the 

 twentieth row on the left of the center with a heptagon on its right ventral border, and column 

 9 originates in a pentagon in the middle in the twenty-ninth row with a heptagon on its left 

 ventral border. This area shows aberrant variations in three adventitious pentagons, P, P, P, 

 each of which bears a heptagonal plate on its left or right border. Dorsally, the adambulacral 

 columns 1 and 2 drop out at the points X, X, above which columns 3 and 4 assume an adradial 

 position. At the point P', column 5 drops out; at P", column 8 drops out, so that above this 

 zone there are only five columns, a case of rather extreme senescence. The apical disc is not 

 preserved. 



This species differs from M. multiporus as it has twelve instead of ten columns of ambula- 

 cral plates in an area, also in that it has high instead of low melon-like ribs. It differs from 

 M. giganteus in that it has nine instead of eleven columns of interambulacral plates in an area, 

 also it has a much less accelerated development than that species. 



Lower Carboniferous, detailed horizon and localitj^ not known, but probably, from its 

 lithological character, from Kentucky or Tennessee. Holotype in Vanderbilt University 

 Collection (Nashville, Tennessee), 220, from which it was kindly loaned me by Professor L. C. 

 Glenn. 



*Melonechinus giganteus (Jackson). 



Text-fig. 237, p. 231 ; Plate 5S, fig. 2; Plate 59, figs. 4, 12-1.5; Plate 60, fig. 3; Plate 61, figs. 5-9. 



Melonites giganteus Jackson, 1S96, pp. 172, 240, Plate 4, fig. 19; Plate 5, figs. 21-24. 

 Melonites muUiporus (pars) Klem, 1904, p. 43. 

 Melonites granulahis Troost in Wood, 1909, p. 107. 

 Melonecliinus giganteus Lambert and Thiery, 1910, p. 121. 



This represents structurally the highest species of the genus and family, and the type is 

 one of the largest and finest of known Palaeozoic Echini. Test high, spheroidal, with strongly 



