MILIOLIDA. 15 
Subgenus—SpiroLocuuina, D’ Orbigny. 
General characters.—Shell consisting of numerous segments arranged spirally on one 
plene. Segments scarcely embracing, so that the whole number are visible on both 
lateral faces. 
1. Sprronocunina pLaNuLATA, Lamarck. Plate III, figs. 37, 38. 
MILIoLitEs PLANULATA, Lam., 1805. Ann. Mus., vol. v, p. 352, No. 4. 
MILIOLA — Defr., 1824. Dict. Nat. Sc., xxi, p. 68. 
SPIROLOCULINA DEPRESSA, D’Orb., 1826. Modele No. 92. Ann. Sc. Nat., vol. vii, p. 
298, No. 1; Soldani, Test. Zooph., vol. iii, p. 229, pl. 155, 
figs. kk. 
= Baprenensts, Jd. 1846. For. Foss. Vien.,p.270, pl. 16, figs. 13—15. 
— DILATATA, Id., 1846. Ib., p. 271, pl. 16, figs. 16—18. 
— EXCAVATA, Id., 1846. Ib., figs. 19—21. 
= concenrRIcA, S: Wood, 1843. Morris’s Cat. Brit. Foss., p. 64. 
— DEPRESSA, Jones, 1854. Ib., 2nd edit., p. 43. 
’ — — var. ROTUNDATA, Williamson, 1858. Rec. For. Gt. Brit., p. 82, 
pl. 7, fig. 178. 
_ PLANULATA, Parker and Jones, 1860. Ann. N. Hist., 3rd ser., vol. v, p. 466 ; 
P. J. and Brady, 1865, ib., vol. xvi, p. 33. 
Characters.—Shell elliptical or oblong, complanate; chambers all visible; margins 
more or less rounded. Length, 3th inch. 
This is the central, sub-typical form of the Spzroloculine. Amongst the fine bold 
specimens belonging to this group there is less variation from the normal condition than 
in any other of the Milioline sub-genera. ‘The chief deviations which we find are those 
arising from feeble growth, giving rise to an elongated starved condition of the shell; or, 
as a result of rapid development from very small central chamber, an extremely bi-concave 
form in the adult. There are also occasional irregularities in the contour of the shell, 
from the much curved or sigmoidal growth of the chambers, and from the hollowing of 
their lateral faces; but the absence of surface-marking from the entire group lessens the 
number of varieties requiring trivial names. 
Spiroloculina planulata is common in the Sutton Crag, and the specimens obtained 
from that source are of good size and of coarse growth. From the Polyzoan Crag we 
have seen only a few small examples. Geologically, Spiroloculine appear amongst the 
