PHOLIDECHINUS. 299 



This species, which I make the type of the genus, is represented only by the specimen 

 described, which was collected by the late Dr. F. A. Randall in the Waverly Group, Lower 

 Carboniferous, of Warren, Pennsylvania. Then it came into the hands of the late Professor 

 Beecher, and by him was transferred to the Yale University Museum Collection. 



Pholidechinus gen. nov. 



Test high, spheroidal; ambulacra narrow throughout, with two columns of plates in each 

 area. Plates low primaries, all alike, or at the mid-zone alternate plates slightly narrowed 

 at the interambulacral contact, and nearly or quite cut off from that area by the marginal 

 enlargement of their fellows. Pore-pairs are uniserial, or at the mid-zone slightly biserial. 

 Ambulacral plates are thin, imbricate adorally, and bevel strongly under the adradials. Inter- 

 ambulacra wide with many (nine to ten in the species known) columns of plates in an area; the 

 plates are polygonal with very rounded outlines and imbricate strongly dorsally and laterally 

 and over the ambulacrals. Both ambulacral and interambulacral plates bear only secondary 

 tubercles and spines. The primordial interambulacral plates are in the basicoronal row, and 

 succeeding columns come in with a slow, not an accelerated development. Peristome with 

 ambulacral plates only, oculars unknowia, genitals low, each with many pores. Lantern low, 

 inclined. 



The type and only known species is P. brauni of the Lower Carboniferous. 



This genus differs from Lepidocentrus in that interambulacral plates bear secondary spines 

 only instead of primary and secondary ; also in that ambulacral plates at the mid-zone are not 

 all alike and pore-pairs are not strictly uniserial as they are in Lepidocentrus. From Hyatt- 

 echinus it differs in that the ambulacra are narrow throughout, instead of broad and petaloid 

 ventrally, and the interambulacra have fewer columns of plates, without marked acceleration 

 of development. 



*Pholidechinus brauni sp. nov. 



Text-fig. 207, p. 184; Plate 27, figs. 1-6; Plate 28, figs. 1-10; Plate 32, fig. 6. 



Of this striking type there is a considerable amount of excellent material. The test is 

 high, spheroidal. In the holotype (Plate 27, fig. 1) the ambulacra measure 5 mm. in width 

 at the mid-zone, and the interambulacra 19 mm. in width. From these measurements the 

 circumference would be about 120 mm. and diameter about 38 mm. The two other specimens 

 figured are somewhat larger. The ambulacra are narrow throughout, with two columns of 

 plates, which are low, imbricating adorally, and laterally strongly beveled under the adambula- 

 crals. The pore-pairs have well marked peripodia. Ventrally the ambulacral plates are pri- 

 maries, all alike, with pore-pairs uniserial. Above this area and at the mid-zone alternate 

 plates differ somewhat, one plate being a pure primary, but enlarged on its outer margin; the 



