72 
THE VOYAGE OF H.M.S. CHALLENGER. 
superior surface, those of the last convolution only on the inferior or apertural side, 
sometimes one face being more convex, sometimes the other. Aberrant forms evolute, 
outspread, acervuline, or irregular. Some of the higher modifications with double 
chamber-walls, supplemental skeleton, and a system of canals. 
Sub-family 1 . Spirillininse, — test spiral, non-septate. 
Test a complanate, planospiral, non-septate tube ; free or 
attached, . . . . . . . . Spirillina, Ehrenberg. 
Sub-family 2. Rotalinse, — test spiral, Rotaliform, rarely evolute, very 
rarely irregular or acervuline. 
Test conical, consisting of an external layer of spirally 
arranged or annular chambers divided into chamber- 
lets ; the interior of the cone filled either with hya- 
line shell-substance or by an aggregation of compressed 
chambers, ...... Patellina, Williamson. 
Test more or less trochoid or complanate. Segments of 
the trochoid forms spiral at the apex, subsequently 
arranged concentrically round a deep umbilical vesti- 
bule with which each chamber communicates by a 
neck. Complanate forms with rows of pores along 
the septal depressions of the inferior surface. Pelagic 
type, with large inflated chamber covering the base 
of the shell, ..... Cymbalopora, Hagenow. 
Test free or adherent, Rotaliform; planoconvex or trochoid 
rarely complanate ; aperture an arched slit, often 
protected by an umbilical flap — the flaps some- 
times forming a whorl of subsidiary chambers. 
Shell somewhat coarsely porous, . . . Discorbina, Parker & Jones. 
Test normally adherent ; compressed or complanate seg- 
ments very numerous ; commencing growth on a 
spiral plan, but subsequently becoming more or less 
cyclical ; the lipped apertures of the individual seg- 
ments opening externally at the periphery. Aberrant 
varieties often wild-growing and irregular, sometimes 
acervuline. Shell- wall coarsely porous, . . Planorbulina, d’Orbigny. 
