MILIOLIDA. 23 
General characters —Shell a flat, circular disk, composed of one or more layers 
of concentric zones arranged around a central or primordial portion. Each zone ot 
chamber subdivided by depressions in the shell wall (marked externally by surface 
furrows) into ovate or rectangular chambers, whose long diameter is m the direction of 
radii. Pseudopodial orifices situated in depressions on the lateral face of the peripheral 
chamber. Texture porcellanous, diaphanous. 
1. Orsiro1iTes orBicuLus, Forskal. Plate III, figs. 45—47, 
Umbilicus marinus, Plancus, 1744. Fab. Columne Lyne. Phytobas. Addit. p. 136, pl. 38, 
fig. F. 
Helicite et Opercule, Guettard, 1770. Mém., vol. iii, p. 434, pl. 13, figs. 30—32. 
Navtitus orsicuLus, Forskal, 1775. Descrip. Anim., p. 125, No. 66. 
ORBITOLITES CoMPLANATA, Lamarck, 1801. Syst. Anim. s. Vert., p. 376. 
Disconiruus X., Fortis, 1802. Mém. Hist. Nat., vol. ii, p. 111, pl. 3, figs. 4, 5. 
Madreporite, Deluc, 1803. Journ. Phys., vol. lvi, p. 349, fig. 9. 
DiscoLiTEs coNcENTRICUS, Montfort, 1808. Conchyl. System., vol. i, p. 186. 
OrBITOLITES PLANA, Brongniart and Cuvier, 1808. Ossem. Foss., vol. ii, part 2, p. 270. 
ORBULITES MARGINALIS, O. compLanatTa, Lamarck, 1816. Anim. s. Vert., vol. ii, p. 196, 
. Nos. 1, 2. 
ORBITOLITES COMPLANATA, Schweigger, 1819. Beobacht., pl. 6, fig. 60. 
ORBULITES PLANULATUS, Blainville, 1825. Dict. Se. Nat., xxxvi, p. 294; Atlas' Zooph:, 
pl. 47, fig. 2; Actinologie, p. 441, pl. 72, fig. 2. 
— MARGINALIS, O. COMPLANATA, Lamourouz, 1821. Gen. Polyp., pp. 44, 45, 
pl. 73, figs. 13—16. 
ORBITOLITES CoMPLANATA, Defrance, 1825. Dict. Sc. Nat., xxxvi, p. 294. 
— — Bronn, 1825. Syst. Urwelt. Pflanz., pl. 6, fig. 18; 1838, Leth. 
Geogn. pl. 35, fig. 22. 
SoritEs orBicutus, Ehrenberg, 1838. Berlin Trans. (1839), p. 112, pl. 3, fig. 2. 
Ampursorus Hempricuil, Ehrenberg, 1838. Ib., p. 114, pl. 3, fig. 3. 
OrBITOLITES COMPLANATA, O. ELLIPTICA, Michelin, 1840—45. Icon. Zooph., p. 167, pl. 46, 
fig. 4, and p. 277, pl. 61, fig. 1]. 
— Carpenter, 1850. Quart. Journ. Geol. Soc., vol. vi, p. 30, pl. 6, 
fig. 23; pl. 7, figs: 24—30. 
OrBicULina (ORBITOLITES) compPLaNaTa, Williamson, 185). Trans. Micr. Soe., vol. iii, 
p. 115, pl. 17, fig. 8;. pl. 18, figs. 9—14. 
ORBITOLITES COMELANATUS, Jones, 1854. Morris’s Cat. Brit. Foss., 2nd edit., p. 39. 
— comPLANATA, Carpenter, 1856. Phil. Trans., vol. cxlvi, p. 181, pls. 4—9; 
1862, Introd. Foram., p. 105, pl. 9. 
— — Parker and Jones, 1860. Ann. N.H., 3rd ser., vol. v, p. 291, &c. 
Characters.—Shell circular, discoidal, flat, sometimes slightly bi-concave. Chambers 
consisting of narrow concentric bands, subdivided into chamberlets, which alternate, after 
the pattern of the Speral of Archimedes (Haughton); surface marked by furrows, indicating 
the margins of the chamberlets. Shell composed of one (simple type) or several (complex 
