MELONECHINUS. . 365 



Melonechinus dispar (Fisclu-r von Wakiheim). 

 Plate 51, figs. 1-8. 



Palechiniis dispar Fischer \on Waldheiin, 1S4S, p. 243, Plate 8, figs. 4a— 4(1 (on the plate there are only 



three figures; all copied liere). 

 Pulechtinus dispar (by typographical error) Fischer von Waldheim, 1S4S, p. 247. 

 Palaeoi'chinuJi dispar Eichwald, 1860, p. 651. 



Melonites dispar Loven, 1874, p. 42; Jackson, 1896, p. 240; Klem, 1904, p. 41. 

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



The test is spheroidal, with moderately elevated melon-like ribs. Ambulacra broad, 

 with six columns of plates at the mid-zone; according to the figures the ambulacral plates are 

 more regular in form and size than in other known species of the genus. In the interambulacra 

 there are four columns of quite high hexagonal and pentagonal plates, which, as figured, bear 

 few small widely spaced secondary tubercles. 



This species has as few columns of ambulacral plates as any in the genus, and also the least 

 number possible to be included in this genus. It has the least number of interambulacral 

 plates of any species with six columns of ambulacral plates, and therefore it is considered the 

 most primitive species in the genus. 



Lower Carboniferous Limestone, Ratofka, Russia, the locality of the type; Carboniferous, 

 "Etage moyen," Moscow, and in Lower Carboniferous of the village of Sloboda, in the Govern- 

 ment of Toula, Russia (Eichwald). 



*Melonechinus parvus (Hambach). 



Plate 51, fig. 4; Plate 52, fig. 1. 



OUgoporus parvus Hambach, 1884, p. 550, Plate C, fig. 3; Keyes, 1894, p. 127; 1895, p. 183; Klem, 1904, 

 p. 40; Lambert and Thie'ry, 1910, p. 121. 



The test is small, .spheroidal, and much compressed in the type specimen. Diameter 

 through B, G, 55 mm. This is doubtless somewhat exaggerated by the vertical compression 

 of the test. Width of ambulacrum B, at the mid-zone, 15 mm.; width of interambulacrum A 

 about 20 mm. 



Ambulacra are wide, with six columns of plates at the mid-zone, one column of wide 

 occluded plates, one of demi-, and one quite irregular column of isolated plates in the middle 

 line of each half-ambulacrum. This character removes the species from OUgoporus in which 

 it was described by Hambach, and places it as one of the lowest species of Melonechinus. 



In the development of the ambulacrum (Plate 52, fig. 1), there are ventrally in area B 

 four columns of plates, narrow demi- and wide occluded. Above this Lovenechinus stage. 



