76 
THE YOYAGE OE H.M.S CHALLENGER. 
Shell typically complanate and planospiral, with the 
whole of the convolutions visible ; the earlier 
whorls more or less embracing. Interseptal and 
marginal canals conspicuously developed, 
Test resembling Operculina in general contour ; chambers 
long and narrow, and divided into chamberlets ; 
aperture a row of pores on the outer septal face, 
Test lenticular or complanate, planospiral, regular. Seg- 
ments equitant, the alar prolongations of each 
convolution completely enclosing the previous whorls. 
Aperture simple, close to the periphery of the 
previous convolution. Supplemental skeleton 
provided with complex canal system, 
Test complanate, structure similar to that of Nummulites , 
but the alar extensions of the chamber-walls thin 
and closely superimposed, so that the outline of the 
convolutions is visible externally, 
Operculina, d’Orbigny. 
Heterostegina, d’Orbigny. 
Nummulites, Lamarck. 
Assilina, d’Orbigny. 
Sub-family 4. Cycloclypeinse, — test complanate with thickened centre, or lenti- 
cular ; consisting of a disk of chambers arranged in concentric annuli, with more or less 
lateral thickening of laminated shell-substance, or acervuline layers of chamberlets. 
Septa double, and furnished with a system of interseptal canals. 
Discoidal layer usually single ; with superimposed 
laminae of finely tubulated shell-substance, thickest 
at the centre, often only slightly developed, . Cycloclypeus, Carpenter. 
Median plane composed of chamberlets arranged in regular 
annuli round a distinct central chamber; thickened on 
either side by layers of flattened chamberlets, more 
or less irregularly disposed, .... Orbitoides, d’Orbigny. 
(Sub-genera — Discocyclina, Rhipidocyclina, Aktinocyclina, Asterocyclina, 
Lepidocyclina, Giimbel.) 
Sub-family 5. (?) Eozooninse, — test forming irregular, adherent, acervuline masses. 
(?) Test adherent, outline irregular ; composed of seg- 
ments arranged at first in more or less regular 
superimposed layers, subsequently acervuline ; with 
interseptal skeleton and ramifying canals, . . Eozoon, Dawson. 
