PHOLIDOCIDARIS. 433 



The characters of this genus are taken from the type species, P. irregularis, the only one 

 yet known with any degree of completeness. Test spheroidal. Ambulacra are moderately 

 wide; ventrally the plates are large, and dorsall}^ much smaller, with many columns of plates 

 in each area (six columns in P. irregularis). Interambulacra are wide, with many columns 

 of plates in each area (five to six in P. irregularis). The interambulacral plates are large 

 and scale-like; the adambulacral plates dorsally are much larger than the plates of median 

 columns. They imbricate strongly aborally, from the center outward, and over the ambula- 

 crals on the adradial sutures. Adambulacral plates (dorsally) bear a large, eccentric, perforate 

 primary tubercle, and in addition, numerous small secondary tubercles. Plates of median 

 columns (dorsally) bear secondary tubercles only. Ventrally apparently all interambulacral 

 plates are similar, each with a perforate primary tubercle (pp. 435, 437, 439). Primordial 

 interambulacral plates are in the basicoronal row, above which additional columns originate, 

 passing dorsallj'. The peristome is not known, but probably was covered with ambulacral 

 plates only as in Lepidesthes (p. 413). Mr. Agassiz (1881, p. 79) speaks of the peristome of 

 Pholidocidaris as if it were known, but I believe it has never been described, and if Mr. 

 Agassiz knew what the structure is, he did not describe it. Oculars are doubtful, genitals 

 large, with numerous pores. There is no evidence that the apical disc of Pholidocidaris is 

 structurally comparable to the apical disc of the Echinothuriidae (p. 414), as assumed by Mr. 

 Agassiz (1881, p. 79). The periproct is unknown. The lantern is inclined, and as far as 

 known, with the typical characters of the Perischoechinoida. 



Type species, Pholidocidaris irregularis (Meek and Worthen) from the Lower Carboniferous 

 of America. 



Kry to the Species of Pholidocidaris} 



Six columns of plates in an ambulacral area and six or five columns of plates in each interambulacral 

 area. Ambulacral plates are large ventrally, small dorsally. Interambulacral plates ventrally of about uni- 

 form size; dorsally, adambulacral plates are wider and higher than plates of median columns. Dorsally, 

 primary tubercles are on adambulacral plates only . . .P. irrrgidaris (Meek and Worthen), p. 434. 



Interambulacral plates, as far as known, are rounded, thin, scale-like, and imbricating, with eccentric 

 primary and secondary tubercles and spines; ambulacral plates are, as far as known, large and rounded, with 

 pore-pairs in the middle of the plates ......../-". tniuis Tornquist, p. 440. 



Interambulacral plates are polygonal, scale-like, and imbricating, with eccentric primary and secondary 

 tubercles; very imperfectly known; Devonian . . . . . .P. acuaria (Whidborne), p. 441. 



Apparently six columns of hexagonal plates in an ambulacral area, and apparently three or more columns 

 of plates in an interamliulacral area, with high, wide, adambulacral plates similar to those of P. irregularis; 

 very imperfectly known .......... /'. gaiidri/i (Julien), p. 442. 



'In regard to the names Pholidocidaris and P. irregnl(iri)i, attention is called to the names Heteroeidaris and //. 

 keokiik and //. lacrispirui under Nomina Nuda (p. 4.50). 



