GENEBA AND GEOUPS OF THE ECHIFOIDEA. 15 



the poles, irregular in shape or hexagonal in the median line and 

 polygonal at the arabulacral edge. Ornamentation of small 

 granules with occasional small bosses surrounded by a flat 

 scrobicule ; plates obliquely bevelled at the edges, admitting of 

 slight overlap. 



Fossil. Carboniferous Limestone : England and Ireland. 



Eamily Melonitid^. 



Perischoechinoida with broad ambulacra composed of many 

 vertical rows of poriferous plates. 



Grenus Melonites, Norwood Sf Owen, 1846, Amer. Journ. 2 ser. 

 vol. ii. p. 225. Meeh Sf Worthen, 1866, Fal. Illinois, vol. ii. 

 p. 227. Quenstedt, 1872-75, Pefr. Deutsch. Abth. i. vol. iii. 

 p. 381, pi. Ixxv. figs. 44-50. Loven, Mudes, 1874, p. 41. 

 i2. Etheridge, Junr., 1874, Quart. Journ. Geol. Soc. vol. xxx. 

 p. 313. W. Keeping, 1876, Quart. Journ. Geol. Soc. vol. 

 xxxii. p. 395. 



Syn. Melechinus, Quenst. 



Test very large, ellipsoidal, grooved longitudinally ; plates 

 thick. 



Apical system central, with five equal, pentagonal, tall basal 

 plates with a corresponding number of intervening radial plates ; 

 genital perforations of the basal plates varying in number from 

 three to five, a single pore to a radial plate. Periproct circular. 



Ambulacra broad, concave on both sides of a median ridge, 

 with ten or more vertical rows of rather geometrical or of small, 

 low, broad plates, thin or thick, each perforated near its centre 

 by a pair of pores, median rows the largest; some slight imbrica- 

 tion of the plates. 



Interradia with seven or eight or nine vertical rows of plates, 

 diminishing in number towards the poles, thick, small, hexagonal 

 near the median lines, pentagonal next to the ambulacra and the 

 edges festooned there for the zigzag of the ambulacral suture. 

 Some obliquity of the edges of the plates, especially when thick. 

 Ornamentation of very small, distant, mamillate, imperforate 

 tubercles ; on the ambulacra they are close, and upon scrobicular 

 circles. Spines minute, acicular. 



Peristome central. Jaws large, and with stout pyramids, 

 teeth large, grooved, and long, pointed. 



