GENERA AISD GROUPS OF THE ECHINOIDEA. 13 



median plate overlapping at its sides its neighbours, and the 

 aboral edge of each plate overlapping the adoral edge of the plate 

 above. Tubercles on each of the plates of the numerous rows 

 above the ambitus, and absent below, except upon the plates 

 nearest the ambulacra, where they are solitary. Dental apparatus 

 unknown. 



Fossil. Upper Devonian and Lower Carboniferous: N. 

 j!^merica. Carboniferous: Europe (Belgium). 



Genus Pal^echinfs, Scouler, MSS. 1839. McCoy, 1844, Synop. 

 Carl. Foss. Ireland, p. 171 (pars). Baily, 1864, Journ. Boy. 

 Geol. Soe. Irel. vol. i. pp. 63-65 ; 1865, Geol. Mag. vol. ii. 

 p. 42. Meeh ^ Worthen, 1866, Fal. Illinois, vol. ii. p. 229. 

 De KonincJc, 1869, Bull. Acad. Brux. vol. xxviii. p. 554. 

 B. Ftheridge, Junr., 1874, Quart. Journ. Geol. Soc. vol. xxx. 

 p. 311, pi. XX. Loven, 1874, Etudes, p. 40. W. Keeping, 

 1875, Quart. Journ. Geol. Soc. vol. xxxii. (1876), p. 37- 

 Duncan, 1889, Ann. Sf Mag. Nat. Hist. ser. 6, vol. iii. 

 p. 196. {Amended.) 



Syn. Protoechinus, Aust. ; TypJilecJiinus, Neum. 



Test moderate to very large, prolate or oblate spheroidal, rigid, 

 thick. 



Apical system central, with a pentagonal periproct sur- 

 rounded by five large basal plates, each perforated by three canals, 

 or one plate may have but one perforation ; five small, doubly 

 perforated radial plates, placed either within the periproctal 

 ring or not separating the basal plates ; the anal membrane with 

 concentric plates, largest externally. 



Ambulacra narrow, straight, convex along the median line and 

 sunken in the poriferous zones, composed of two vertical rows of 

 very numerous low, thick plates of different shapes ; these are 

 either primaries, all of which reach the ambulacro-interradial 

 suture as well as the median ambulacral suture, or alternate 

 plates which are more or less blocked out from the inter- 

 radial suture, by the increased dimensions of the outer parts of 

 the plates above and below ; or there may be demi-plates and 

 more or less perfect primaries in the same ambulacrum, the demi- 

 plates being large at the interradial suture and short and pointed 

 towards the median ambulacral line, the primaries being long and 

 may not reach the interradial suture ; compound plates rare. 

 Pairs of pores, in two vertical rows, on each side of an ambu- 



