MELONECHINUS. 367 



The interambulacra are a little wider than the ambulacra, arching from the adradial sutun-s 

 outward in relatively high melon-like curves. In each area there are six columns of plates at 

 or a little above the mid-zone. In areas E, G, and I there are only six columns, but in A and C 

 a seventh column is represented by a few plates dorsally in the middle line of each area (Plate 

 52, fig. 2). Interambulacral and ambulacral plates alike bear small secondary tubercles with 

 corresponding small spines about 3 mm. long. Ventrally, in Plate 52, fig. 4, the first three 

 rows of interambulacral plates are restored, as indicated by dotted lines. Assuming that these 

 are correct, the fifth column originates in a pentagonal plate in the seventh row, with a heptagon 

 on its left ventral border. The sixth column originates in the eleventh row with a pentagon, 

 on the right of the center, and bearing a heptagon on its left ventral border. Dorsally, the 

 adradial columns 1 and 2 drop out before reaching the apical disc, indicating senescence. The 

 apical disc is imperfectly preserved, but the diameter as closely as it can be ascertained is about 

 7.5 mm., which is proportionately about 23% of the diameter of the test. This is proportion- 

 ately larger than in more specialized species as M. multiporus and M. liratus in which the 

 diameter of the apical disc is only 13 to 16 % of the diameter of the test. An ocular plate in 

 place covers the ambulacrum and laterally in part the interambulacra on either side. Two 

 genital plates lie against the ocular, one twisted out of place and in part covering the ocular. 

 Genital pores are not shown. 



This species is one of the smallest known in the genus, yet the type represents an adult, 

 or even old-age individual, as indicated by the dropping out of adambulacral columns dorsally. 

 As regards the ambulacrum, it is one of the simplest species known in the genus, but in its 

 interambulacral structure is more specialized than the two previously described species. I take 

 pleasure in naming this species for Mr. Frank Springer, the eminent crinoid specialist, who 

 generously loaned me his whole collection of Palaeozoic Echini, which has been an invaluable 

 aid in my work. 



St. Louis Group, Lower Carboniferous, Elizabethtown, Kentucky, F. Springer Collection 

 8,103. 



*Melonechinus crassus (Hambach). 



Plate 51, fig. 6; Plate 52, figs. 7-11. 



Melonites crassus Hambach, 1884, p. 548, Plate C, fig. 1; Keyes, 1894, p. 126; 1895, p. 182; Jackson 



and Jaggar, 1896, p. 137; Jackson, 1896, p. 240; Klem, 1904, pp. 8, 41, Plate 1, figs. 2a-2d. 

 Melonechinus crassus Lambert and Thiery, 1910, p. 120. 



The test of this fine species is high and spheroidal, with strong, rounded, melon-like ribs 

 in ambulacral and interambulacral areas. Known only from the type specimen (Plate 51, fig. 

 G), which is compressed and with a dorso-ventral thrust. Height of the test about 90 mm., 

 diameter about 111 mm., but this measurement is somewhat exaggerated by lateral compres- 



