412 ROBERT TRACY JACKSON ON ECHINI. 



surmounting the interambulacrum. The pores cannot be distinguished in the photographic 

 figure. This is all that is known of the apical disc in this species. 



Professor Fraipont says that he'had twelve specimens, so that it is evidently quite abundant 

 where found. He referred his specimens to the genus Oligoporus, comparing the ambulacrum 

 with that of my Oligoporus ( = Lovenechinus) missouriensis, see text-fig. 244, p. 338, of this 

 memoir. Structurally, as regards this character, the comparison is apt, but other characters, 

 as imbrication of plates and two kinds of tubercles and spines, remove this species from Oligo- 

 porus or Lovenechinus, and all other genera of the Palaeechinidae as well. The characters are 

 very distinctive and do not fit into any known genus of Palaeozoic Echini except Proterocidaris, 

 as discussed under consideration of the genus. 



De Koninck's type specimen is from the Lower Carboniferous of Loyers, Belgium. Frai- 

 pont's specimens are from the Lower Carboniferous, Marbre Noir, of Dinant, Belgium. 



LEPIDESTHES Meek and Worthen. 



Lepidesthes Meek and Worthen, 1868a, p. 522; Loven, 1874, p. 42; Duncan, 1889a, p. 16; Jackson, 1896, 



p. 241; Tornquist, 1897, p. 732; Klem, 1904, p. 24; Lambert and Thiery, 1910, p. 123. 

 Lepidestes Neumayr, 1881, p. 151. 

 Hybochinus Worthen and Miller, 1883, p. 331; Duncan, 1889a, pp. 16-18; Tornquist, 1897, p. 732. 



Test spheroidal, elliptical, or obovate, exceptionally with elevated rounded ribs (L. cari- 

 nata). Ambulacra very wide at the mid-zone, with in each area from eight to sixteen columns 

 of plates, which consist of occluded plates that meet the middle of the area, demi-plates that 

 meet the interambulacra laterally, and, in addition, from two to six regular columns of isolated 

 plates in each half-area. Ambulacral plates are all small, uniform in size, and rhombic or hexag- 

 onal in shape (Plate 70, figs. 1-3), imbricating adorally, and laterally beveled strongly under 

 the adambulacrals. Pore-pairs are in peripodia, situated in each plate above the middle, and 

 in the middle line or more typically nearer the next adjacent interambulacrum than the middle 

 of the plate. Ambulacral plates bear many secondary tubercles and spines but no primaries 

 (Plate 67, figs. 8, 10). As seen from the interior of the test, ambulacral plates imbricate aborally 

 and bevel over the adradials laterally, and pore-pairs are about in the middle of each plate. 

 For comparison of imbrication seen from the exterior and interior, see text-figs. 32 to 38, p. 75, 

 where these relations are shown. Ventrally, near the peristomal border there are four columns 

 of ambulacral plates as a stage in development (Plate 68, fig. 3), above which area the number 

 of columns increases to the full number at the mid-zone. Dorsally, as a localized stage in devel- 

 opment, there is a very simple condition of the ambulacrum next to the ocular plates (Plate 68, 

 fig. 5; text-fig. 251, p. 428), and from this area passing ventrally toward the mid-zone the 

 number of columns increases to the full specific number. 



The interambulacra are very narrow at or near the mid-zone with in each area from 

 three to six columns of small plates of uniform size that imbricate strongly aborally and from 



