364 ROBERT TRACY JACKSON ON ECHINI. 



Melonechinus occurs in the Lower Carboniferous of America, Great Britain, and Russia. 

 The type species is Melonechinus multiporus (Norwood and Owen). 



Key to the Species of Melonechinus. 1 



Six columns of ambulacral and four columns of interambulacral plates in each area 



M. dispar (Fischer von Waldheim), p. 365. 



Six columns of ambulacral plates, and at the mid-zone five columns of interambulacral plates, a sixth 

 column coming in dorsally in each area M. pnreus (Hambach), p. 365. 



Six columns of ambulacral plates, and six columns of interambulacral plates at or just above the mid-zone, 

 with a strong tendency to adding a seventh column dorsally in each area . M. springeri sp. nov., p. 366. 



Eight columns of ambulacral and six columns of interambulacral plates in each area, melon-like ribs low, 

 gently rounded M. crassus (Hambach), p. 367. 



Eight columns of ambulacral and six columns of interambulacral plates; a seventh interambulcral 

 column may appear dorsally, or exceptionally, even an eighth column in each area; melon-like ribs high, 

 sharply elevated M. indianensis (Miller and Gurley), p. 369. 



Eight columns of ambulacral plates and seven (or in one area of the type, six) columns of interambulacral 

 plates in each area. Melon-like ribs strongly and sharply elevated . . M. fttewartii (Safford), p. 371. 



Eight columns of ambulacral and seven columns of interambulacral plates at the mid-zone in each area; 

 test small . M. srptcnarius (Jackson), p. 373. 



Ten columns of ambulacral and three columns of interambulacral plates in each area; test obovate 



M. obovatus sp. nov., p. 373. 



Ten columns of ambulacral and eight columns of interambulacral plates in each area; high, steeply 

 rounded, melon-like ribs in ambulacral and interambulacral areas . . . M. liratus sp. nov., p. 374. 



Ten columns of ambulacral and dorsally eight or nine columns of interambulacral plates (rarely seven 

 columns only in an area) in each area; low, rounded, melon-like ribs in ambulacral and interambulacral 

 areas ........... M. multiporus (Norwood and Owen), p. 375. 



Twelve columns of ambulacral and six columns of interambulacral plates in each area; melon-like 

 ribs wanting M. hce-pingi sp. nov., p. 384. 



Twelve columns of ambulacral and seven columns (possibly more) of interambulacral plates in each area; 

 melon-like ribs wanting M. ethrridgi! (Keeping), p. 385. 



Twelve columns of ambulacral and nine columns of interambulacral plates in each area; melon-like 

 ribs strongly developed M. mndrrhilti sp. nov., p. 388. 



Twelve columns of ambulacral and eleven columns of interambulacral plates in each area; melon-like 

 ribs strongly developed M. gigantcus (Jackson), p. 389. 



1 M elonites ( = Melonechinus) youngi, of which no description has been published, is considered under Nomina Nuda, 

 p. 457. 



