194 
THE VOYAGE OF H.M.S. CHALLENGER. 
ventricosa, Reuss, and Hauerina circinata, Brady, furnish intermediate links con- 
necting the new group with Biloculina and Hauerina ; but these need be no obstacle 
to a generic subdivision otherwise practically convenient. 
Further research has shown that there exist a number of species, heretofore 
assigned to Hauerina and Quinqueloculina, which share the more important general 
characters of Planispirina communis and Planispirina contraria, and it has been found 
needful to devise a generic description in somewhat broader terms than would have 
sufficed for these two forms alone. To this end I propose the following amended 
characters : — 
Planispirina, Seguenza. 
Test free, spiral, compressed; discoidal, crosier-shaped, or oblong ; segments numerous : 
in the earlier stages either helicoid and non-septate (like Cornuspira ), or segmented, 
the chambers being arranged on the Milioline plan ; at a later period either planospiral 
(followed in some instances by a few segments arranged in a right line) or Milioline : 
the inner margin of each successive convolution spreading more or less over the lateral 
surfaces of the test, and producing a laminated condition of the walls. Aperture simple, 
variable in form, but not cribrate or porous. 
Inasmuch as the number of segments in each convolution varies at different periods 
of the growth of the test, it is manifest that the distinction between Planispirina and 
a. b. 
Fig. 5. — Transverse Sections of Planispirina;. 
Planispirina Planispirina Planispirina 
contraria, exigua, sigmoidea, 
x 40 cliam. x 80 diam. x 40 diam. 
Miliolina must rest chiefly on the Nummuline lamination of the shell-wall ; and the same 
character together with the simple orifice serves also to distinguish the former from 
Hauerina. 
The foregoing woodcuts illustrate this peculiar feature of the genus in its different 
