9 



The form is strono;ly melon-like. The vertical height is two 

 and two-tenths inches, and the transverse diameter two and 

 six-tenths inches. The silicification destroj'ed the tubercles and 

 all evidence of spmes. 



The interambulacral areas are somewhat lance-elliptical, in 

 outline, abruptly elevated from the ambulacral depressions, 

 sharplj' rounded at the apical pole, and broadly rounded near 

 the basal extremity, and flattened on the outer face, throughout 

 the whole length. There are seven ranges of plates at the mid- 

 dle part, including the two that dip down into the ambulacral 

 depressions on the sides, or five occupy the flattened surface on 

 top. One of the middle ranges is short, another soon gives 

 way to the narrowing of the area, and while five reach near the 

 basal extremity, only three extend toward the apical end to 

 unite with a genital plate. 



Ambulacral areas only half as wide, in the middle part, as the 

 interambulacral areas, and of almost uniform width throughout 

 their entire length, tapering only slightly as they approach the 

 summit and ocular plates. They are separated in each ambu- 

 lacral field by a sharply defined ridge, elevated as high or rather 

 above the interambulacral areas. The plates are very small in 

 the ambulacral depressions and each one is pierced with a pair 

 of circular pores. There are two ranges of these ambulacral 

 pores in each depression throughout the entire length, and, in 

 the middle part, there seem to be additional pores, but their 

 extent is not exactly determined. 



This species will be readily distinguished from Melonites in- 

 dianensis, by the flattened interambulacral areas, and from it 

 and all other described species, in that genus, by the narrow 

 ambulacral areas, with almost uniform width, and by the two 

 ranges of pores in each depression. We do not know the plates 

 that cover the summit or tlie base of either Melonites or Oliffo- 

 porus. Notwithstanding, Prof. Hambach (Trans. St. Louis 

 Acad. Sci. Vol. IV. p. 549) has examined over 500 specimens of 

 Melonites nuiltiporus, and described new species of Melonites 

 and Oligoporus, these important plates remain unknown. It is 

 wholly unnecessarj^ to compare this species with any other in 

 the genus, because it is not only from a different group of rocks, 

 but it is widely different in form from all of them. 

 -2 G. 



