MELONECHINUS. 369 



*Melonechinus indianensis (Miller ami Giirley). 

 Text-fig. 237, p. 231; Plate 51, figs. 7-9; Plate 53, figs. 1-4. 



Melonites indianensis Miller and Gurley, IS94, p. 5, Plate 1, fig. 1; Jackson, 1890, p. 240. 

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

 Melonechinus indianrnsis Lambert and Thiery, 1910, p. 121. 



A relatively small species, the type being the largest known individual. Test spheroidal, 

 with sharply elevated melon-like ribs in ambulacral and interambulacral areas. The holo- 

 type (Plate 51, fig. 7) measures 54 mm. in height, 67 mm. in diameter at the mid-zone through 

 the axis J, E; width of the ambulacra at the mid-zone 16 mm., width of the interambulacra 

 21 mm. 



The ambulacra are wide, at the mid-zone with eight columns of plates composed of wide 

 occluded, narrow demi-, and two irregular columns of isolated plates in each half-area (Plate 

 53, fig. 3). The occluded plates medially are arched up in a high, rounded, melon-like ridge. 

 Pore-pairs are in deep valleys on either side of the ambulacral areas, each pair in a well marked 

 peripodium, situated in the lateral portion of each plate. In the developing area ventrally 

 (Plate 53, fig. 2) there are near the peristomal border two columns of plates, narrow demi- 

 and wide occluded in a half-area. Higher up, as shown, isolated plates appear in the middle 

 line of the half-areas as a second stage, then isolated plates become continuous so as to form one 

 column, repeating in this stage the character of species like springeri that typically have only 

 one isolated column. Then a second isolated column appears, fixing the species character in 

 this feature. Dorsally, as localized stages in development, near the apical disc (Plate 53, fig. 1) 

 there is a single column of primary plates in each half-area. Ventrally, they pass quickly into 

 stages of two columns, then three, and finally four in a half-area. These ventral and dorsal 

 stages and their relations to lower genera and species are set forth diagrammatically in text-fig. 

 237, p. 231. The dorsal localized development of indianensis is more accelerated than in the 

 lower species, springeri, as in that region the Oligoporus stage of scattei'ed isolated plates is 

 skipped in indianensis although ventrally this character is retained as a developing stage. 



The interambulacra of indianensis are slightly wider than the ambulacra, and are rounded 

 up in high, wide, melon-like ridges which laterally dip suddenly down to the adradial sutures. 

 In the type there are six columns of plates in four interambulacral areas. A, C, E, and G, but 

 in area I (Plate 53, fig. 4), as an exception, there are seven columns and even an eighth is repre- 

 sented by two plates. This is evident!}' a progressive variation, not common in the species, 

 since in two other specimens here figured all the areas have six columns only. In this unusual 

 area (Plate 53, fig. 4) the basicoronal row and a few plates on either side are restored as indi- 

 cated by dotted lines. There are three plates in the second row, and four in the third. The 

 fifth column originates in the middle in the seventh row with a tetragonal plate, which is very 



