288 ROBERT TRACY JACKSON ON ECHINI. 



"Lepidocentrus rhenanus (Beyrich). 

 Plate 20, fig. 7. 



Pdaechimts rhmanus Beyrich, 1857, p. 4; Quenstedt, 1875, p. 377, Plate 75, fig. 18. 1 

 Lepidocentna rhenanus Miiller, 1857, p. 264, Plate 4, figs. 4-6; Loven, 2 1874, p. 40; Jackson, 1896, p. 244; 

 (pars) Klem, 1904, p. 17; Lambert and Thiery, 1910, p. 122. 



Test spheroidal, ambulacral plates low. Interambulacrum with five columns of plates 

 which are nearly hexagonal, as seen in area E of Plate 20, fig. 7. The primordial interambulacral 

 plate is in the basicoronal row, and from this it is inferred that the same occurs in other species 

 of the genus. Columns 2, 3, 4 originate in succeeding rows of plates, and column 5 appears in 

 the sixth row. There are powerful jaws in place ventrally. The type and only known speci- 

 men, which is in the Berlin Museum fur Naturkunde, is an internal mold, and therefore the 

 external character of the plates is unknown. The plates also are probably more hexagonal in 

 outline than they would be on the exterior (compare text-figs. 32-34, p. 75). 



Devonian, Wipperfiirth, Prussia. 



*Lepidocentrus drydenensis (Vanuxem). 

 Plate 16, fig. 5; Plate 21, figs. 1-3. 



Echinus drydenensis Vanuxem, 1842, p. 184. 



Eocidaris drydenensis Hall, 1868, p. 298; 1870, p. 341; Loven, 1874, p. 43; Klem, 1904, p. 71. 



Archaeocidaris drydenensis Keyes, 1895, p. 184; Jackson, 1896, p. 214. 



This species has never been figured before, and, as indicated in its synonymy, has been 

 variously placed generically. The type, which may be considered the best preserved individual, 

 is on a large slab with the faint impressions of two or more other individuals. The plates them- 

 selves are not preserved, but we have an impression only with the plates entirely dissolved 

 away. This is true of the spines as well as the plates. The best impression is fortunately 

 of the ambulacral areas and of the spines, while the impression of the interambulacral areas 

 is for the most part weak and ill defined. Diameter through J, E, 70 mm., also through H, C. 

 The view, which is ventral, shows a rather deep depression in the oral region. Diameter of 

 the peristome 6 mm. The shape of the test was doubtless spheroidal, or spherical. Ambula- 

 cral areas narrow, plates low, about seven or eight equaling the height of an adambulacral 

 plate. Ambulacral pore-pairs lie near the next adjacent interambulacrum and are on an angle, 

 the outer pore a little higher than the inner; width of an ambulacrum at the mid-zone 14 mm. 



1 Non Palaeocidaris rhenanus Quenstedt, 1875, p. 377, Plate 75, figs. 30-37 (for which in this memoir see Xenocidaris 

 clavigera). 



2 Lov6n writes " L.[epidocentrus] rhenanus (Palaeocidaris) Beyrich," thus indicating that Beyrich put the species in 

 Palaeocidaris, which is a mistake, as he put it in Palaechinus. Palaeocidaris rhenanus is Qucnatedt's name, applied to 

 another species; here referred to Xenocidaris clavigera as a synonym, see under Incertae Sedis. 



