394 ROBERT TRACY JACKSON ON ECHINI. 



The peristome where known has ambulacral plates only. Oculars are insert or exsert, 

 and imperforate or exceptionally with one pore (Lepidechinus, Plate 63, fig. 8), or two pores 

 (Lepidesthes formosa, Plate 68, fig. 5) . The oculars ventrally cover the ambulacra and laterally 

 the interambulacra in part on either side. The genitals are high and wide with from one (Lepi- 

 dechinus, Plate 63, fig. 8) to many pores each. A madreporite is clearly existent in some 

 species. Plates of the periproct are numerous and angular, much as in other Palaeozoic types. 

 The lantern is inclined, teeth grooved, pyramids wide-angled, with moderately deep foramen 

 magnum; epiphyses are narrow, capping the half-pyramids, and braces are of the character 

 usual in all regular Echini. 



LEPIDECHINUS Hall. 



1 Lepidechinw Hall, 1861, p. 18; (pars) 1868, p. 295; (pars) 1870, p. 339; (pars) Loven, 1874, p. 44; 



A. Agassiz, 1874, p. 648; non 1892, p. 74; (pars) Duncan, 1889a, p. 12; (pars) Keyes 1895, p. 192; 

 (pars) Jackson, 1896, pp. 226, 242; (pars) Klem, 1904, p. 20; (pars) Lambert and Thiery, 1910, p. 122. 



2 Rhoechinus Keeping, 1876, p: 37; (pars) Duncan, 1889, p. 205; 1889a, p. 14; (pars) Jackson, 1896, pp. 200, 



239; (pars) Tornquist, 1897, p. 18; (pars) Klem, 1904, p. 27; Lambert and Thiery, 1910, p. 122. 



Test spheroidal, ambulacra narrow with two columns of plates in each area throughout. 

 Plates all primaries, pore-pairs uniserial or slightly biserial at the mid-zone. The ambulacral 

 plates imbricate moderately adorally, and laterally bevel under the adradials. Interambula- 

 cra are wide at the mid-zone with from four to eight columns of plates in each area in the known 

 species. Interambulacral plates are relatively thick, rounded somewhat in outline, but pentag- 

 onal in adambulacral and hexagonal in median columns. They imbricate aborally and from 

 the center outward and over ambulacrals on the adradial sutures. The primordial interam- 

 bulacral plates are in the basicoronal row (Plate 64, fig. 1). The surface of interambulacral 

 plates bears secondary tubercles only. Peristome with ambulacral plates only. Apical disc 

 as known in one species (Plate 63, figs. 7, 8) with oculars exsert, each with one pore, at least as 

 seen from within, and genitals high and wide, each with one pore. As the apical disc is 

 known only from one specimen, and that one seen from within (Plate 63, figs. 7, 8), it is quite 

 possible that an external view or other species might show other characters. Periproctal 

 plates are unknown. The lantern is inclined, teeth grooved, and pyramids wide-angled, with 

 moderately deep foramen magnum. 



The type species is Lepidechinus imbricatus Hall, from the Lower Carboniferous of America. 



1 Lepidechinus as here described includes L. imbricatus Hall, the type, but not L. rarispinus Hall, which is referred to 

 the genus Hyattechinus, p. 292. 



2 Rhoechinus as used by Duncan includes R. irregularis Keeping, here referred to Lepidechinus, and also species of Palao- 

 echinus, p. 303. In this he was followed by Jackson (1896), Tornquist (1897), and Miss Klem (1904). Lambert and 

 Thie'ry (1910, p. 123) point out this error in the application of the name Rhoechinus. 



