REPORT ON THE FORAMINIFERA. 
625 
Turning now to the Sub-family Rotaljna : — As may be inferred from what lias been 
-already stated, Pcitellina exhibits the nearest approach to the Spirilline simplicity of 
structure. In certain cases the test of Patellina consists partially or entirely of a non- 
septate or imperfectly septate spiral tube, the coils of which are disposed so as to form a 
cone ; but in more typical specimens, and in all the larger species, the outer layer is con- 
structed of distinct spirally-arranged or annular segments, subdivided into chamberlets, 
and the centre of the cone is filled either with a deposit of clear shell-substance or with 
a mass of closely-packed minute chambers. The allied genus Cymbalopora presents a 
structure in many respects similar, the conical varieties being composed of small 
segments, arranged spirally at first but subsequently in annuli, each segment commu- 
nicating with a central or umbilical hollow, the weaker varieties assuming a depressed 
or irregularly spreading contour like the true Planorbulince. 
The genera Discorbina, Planorbulina, Pulvinulina, and Rotcdia, which, so far as 
number of species or abundance of individuals is concerned, constitute the bulk of the 
Family, form four parallel groups, the mutual relationship of which is best understood 
by a comparison of their collateral species. The closest affinity in every case subsists 
between the different members of the same series, and the most correct view of each 
genus is obtained by grouping the species round a central type, of which they are 
regarded as the successive modifications. The types selected for the purpose by Profs. 
Parker and Jones, to whose researches we are largely indebted for our present knowledge 
of this portion of the subject, are Discorbina turbo, d’Orb., sp.; Planorbulina farcta, 
F. and M., sp.; Pulvinulina r&panda, F. and M., sp.; and Rotalia beccarii, Linne, sp. 
The degree of resemblance between the corresponding varieties or “ isomorphs ” of the 
parallel series varies greatly in different cases. In some it is an agreement in little else 
than external contour, whilst in others the likeness is sufficient to be a source of difficulty 
in determining the generic position of specimens; but it is seldom that the true relationship 
is not betrayed by the presence, to a greater or less extent, of some of the conspicuous 
characters of the typical form. 
What is known as a “ Rotaline ” or “ Rotaliform “ shell is one consisting of numerous 
segments arranged in an inequilateral spire, the whole of the segments being visible on 
one side of the test, those of the outermost convolution only on the other. In some cases 
the superior 1 or spiral face is convex or conical and the inferior flat ; in others the two 
1 The terms “ superior ” and “ inferior,” as applied to the Eotalid^e, are used in the sense defined by Williamson, 
as follows : — “ The primordial segment usually occupies the apex of each trochoid form ; and to the lateral surface on 
which this segment appears may he assigned the term superior ; whilst the opposite one, or that in the direction of 
which the animal is extending its growth, may he designated the inferior lateral surface. There are a few exceptional 
cases, as, for example, the British Truncatulince, and the foreign genus Faujasina [ Rotalia schroeteriana ], which simply 
represent an equilateral or nautiloid shell cut in half, the intersection being in the plane of the centre of the primordial 
segment. Hence the surface in the centre of which the primordial segment appears instead of being conical, is flat ; 
whilst the opposite one, in which the animal is extending itself, is more or less conical ; the former being that by 
which the animal attaches itself to other bodies. Notwithstanding the apparent incongruity of applying the terms 
