ON THE GENUS POLYMORPHINA. ' 207 
- General Characters.—Shell free, or (rarely) adherent; globular, ovate, oblong, cylin- 
drical, compressed, or complanate. Visible segments variable in number—two or many. 
Segments even-margined or ventricose; arranged in an obscure spiral or (less frequently) 
in two opposed alternating series (as in Textularia), more or less embracing, and par- 
tially investing the previous segments. Shell inequilateral, from unequal overlapping 
of the segments. Septal lines often depressed, obscure in thick-shelled specimens, but 
in hyaline individuals marked by whitish milky lines. Pseudopodial orifice at the ante- 
rior extremity of the ultimate segment; nearly central, and generally situated in a 
mamilliform protuberance; circular, oval, slit-like, or porous, and (normally) surrounded 
by a coronal of strongly defined radiating grooves. In rare cases the direction of the 
aperture is reversed, as in the Entosolenian Lagene. Texture hyaline and delicate in 
young specimens, opaque and coarse in older ones; never arenaceous. Foramina con- 
spieuous in hyaline shells, minute and tubular in those with thicker walls. Surface 
either smooth or presenting outgrowths in the form of sete, spines, tubercles, granular 
lines, striæ, or riblets. 
The natural position of the genus Polymorphina is in the suborder PERFORATA, Family 
LAGENIDA (Carpenter), between the genera Nodosarina and Uvigerina. 
Whilst there is little difficulty in distinguishing well-grown specimens pertaining to 
this group in any of the numerous modifications of form they are liable to assume, it must 
be borne in mind that there is scarcely a genus in the whole family of Lagenida which has 
not its isomorph amongst the Polymorphinæ. The minute globular forms, either smooth, 
as in the smaller examples of P. gibba, or with ornamented shell like P. myristiformis, 
have a strong resemblance to corresponding varieties of Lagena, especially if the septation 
be obscured, as it often is by a thickened shell-wall; and in these cases the inequilateral 
contour of the shell supplies the best indication of zoological affinity. In P. Soldanii we 
find an acervuline packing of the chambers; and when this occurs in tolerably regular 
series a striking analogy to the smooth Uvigerine is the result. In the Dimorphine va- 
rieties, which are sufficiently distinct to be roughly separated into a subgenus, the mode of 
growth simulates Nodosaria, Bigenerina, or Sagrina; and in addition to these the genus 
presents isomorphs of at least two other types—namely, of Textularia in many of the 
biserial varieties, and of Bulimina in one or two irregular forms described by D'Orbigny. 
But the chief difficulty in diagnosis arises not out of well-developed specimens, however 
much they mimie collateral types, but in modifications arising, on the one hand, out of an 
exaggerated condition of otherwise normal characters, or, on the other, out of the want 
of distinctive character resulting from external influences unfavourable to vigorous 
growth. Better examples of this latter *' starved ” condition could not be found than in 
the assemblage of few-chambered, ill-grown, elongate varieties upon which M. Terquem 
has founded his “ Fourth Memoir on the Foraminifera of the Lias." It is not necessary 
here to occupy space by criticism on a memoir so unsatisfactory; but we may in passing 
enter a protest against the establishment of a number of species on a set of poorly deve- 
loped and sometimes even monstrous individuals. Some of M. Terquem’s drawings do 
not represent Polymorphine at all, but specimens belonging to widely differing genera, 
as Lituola; others are just as likely to be weak and irregularly grown Nodosarine, whilst 
