210 R. T. JACKSON — STUDIES OP PAL.EECHINOIDEA. 



to the tabulations of Mclonites multiporus (catalogue numbers 2992 and 

 3004, on page 170 of the preceding paper). In Lepidesthes coreyi after the 

 fifth, a sixth column is introduced in the seventh row by a pentagon, 

 with an octagonal plate on its right ventral border. Column 6 originates 

 with 2 columns on its left and three on its right, and is therefore one 

 column too far to the left according to the rule of ideal arrangement. 

 The fact of an octagonal plate next a terminal pentagon is abnormal, but 

 there is considerable irregularity in the plates at this area, as the plate 

 below the octagon which might have 6 sides has 7 and a plate to the left 

 of this heptagon is pentagonal, although not a terminal plate of a column. 



Lepidesthes formosus, Miller, is represented by the author of the species 

 (33) by an especially good figure, which adds to the knowledge of 

 generic features by showing genital and ocular plates, both of which 

 are perforated. Miller describes the ambulacral plates as imbricating 

 downward, Avhile the interambulacral imbricate .upward and outward. 

 Both this species and Lepidesthes coreyi also have the pores situated in the 

 middle rather than the outer side of the ambulacral plates. The pub- 

 lished figure of Lepidesthes Jormosus does not show the introduction of any 

 new columns of plates, the full number, 5, extending as far ventrally as 

 the specimen is preserved. 



Lepidesthes colletti, White, is a remarkable species, having, according to 

 its author (41), 18 or perhaps 20 rows [columns] of ambulacral plates. 

 This is a most unusual number, no other echinoid known having more 

 than 12 or 14 columns of ambulacral plates, which number is ascribed 

 to MeJonltes etherldgll^ W. Kee[)ing (21 ). Lepidesthes coUetti in this feature, 

 then, is the most highly specialized species of all Echini. The interambu- 

 jacra, however, do not show any extravagant development, there being 

 only 4 or 5 columns, as descrii)ed. The types of Lepidesthes formosus and 

 coUettl are in the private collection of Mr Wm. F. E. Gurle}^, of Spring- 

 field, Illinois. 



'J'he plate arrangement of interambulacral plates of Lepidesthes^ then, 

 as gathered from the descrijDtion and figure of Lepidesthes coreyi^ agrees 

 with that of Melonites, Ollgoporus and Pcdseechlnus, having only such varia- 

 tions as have been alread}'' met with in Melonltes. 



DESCRIPTION OF PIIOLIDOCIDARIS MEEK/, SP. NOV. 



*• 

 Plate 9, figure 54. 



The genus Pholldooidaris, Meek and Worthen was instituted by the 

 authors for a single s])ecies P. irregularis^ M. and W (31). The type of 

 this species is in Illinois State Museum at Springfield, Illinois ^see foot- 

 note, page 207). The material as described and figured was limited and 

 wanting in some essential characters. It is with satisfaction, therefore, 



