12 PEOF. P. M. DUNCAIf's EEVISION OF THE 



Genus Lepidocidakis, Meeh Sf Worthen, 1869, Proc. Acad. Nat, 

 Sci. PUlad. p. 79 ; 1873, Geol. Illinois, vol. v. p. 478, 

 pi. ix. fig. 15. 



Syn. Eocidaris, sensu, Meek & "Worthen. 



A fragment of a very large test, spheroidal, depressed. Am- 

 bulacra narrow, slightly convex ; plates in two vertical rows 

 feebly imbricated adorally, compound; the primaries alternate 

 with demi-plates, which are pointed towards the median suture. 



Interradia very broad, with eight or nine vertical rows of plates 

 or even more, hexagonal towards the median line and pentagonal 

 close to the ambulacra, all imbricated aborally and laterally ; but 

 the lateral overlap is from the ambulacral edge to the central 

 plates, which are overlapped on either side. A large central 

 tubercle on each interradia! plate, with a small, perforated, central 

 projection for the spine ; the base of the tubercle surrounded by 

 a circular smooth depression, bordered with granular mamelons. 

 Primary spines long, cylindrical, slender, finely striated ; articular 

 end perforated and swollen so as to form a distinct ring. Dental 

 apparatus with the teeth grooved. 



Fossil. Lower Carboniferous Limestone : N. America. 



Grenus Lepidechinus, Hall, 1861, Descr. neio sp. Grinoidea, 

 Prelim, note, Albany, p. 18 ; 1867, Twentieth Beport State 

 Cabinet New York, p. 295. Meelc Sf Worthen, 1866, Geol. 

 Surv. {Pal.) Illinois, vol. ii. p. 294 {reference to Sail). 

 MeeJc Sj- Worthen, 1868, Geol. Illinois, vol. iii. p. 522 (note). 

 Loven, 1874, Etudes, p. 44. P. Etheridge, Junr., 1874, 

 Quart. Journ. Geol. Soc. vol. xxx. p. 312. Keeping, 1875, 

 Quart. Journ. Geol. Soc. 1876, vol. xxxii. p. 36. 



Test large, spheroidal. 



Apical system pentagonal, made up of several ornamented 

 plates, also a circle of small plates within the periproctal ring. 



Ambulacra narrow, straight, with two vertical rows of small, 

 low, broad plates imbricating, the adoral edge of one plate over- 

 lapping the aboral edge of the plate below it. A pair of pores 

 to each plate. 



Interradia very broad, composed of from nine to eleven vertical 

 rows of plates, diminishing considerably in number apically, the 

 plates nearest the ambulacra smallest ; the plates imbricating 

 laterally from the median series and from pole to pole, the 



