12 
DE. CAEPENTEE’S EESEAECHES ON THE EOEAAIINIEEEA. 
ceeded so far as to produce a number of separate branching apertures, and nothing 
is wanting but the removal of the line of shell which passes down the middle of the 
septum, to unite these into the most characteristic form of the single ramifying orifice. 
This individual, like the one represented in fig. 6, was already beginning to assume the 
Spirolim foi-m, the rounded shape of the mouth showing that the spire has detached 
itself completely from the previously-formed convolutions : in figs. 4 and 11 a are shown 
the mouths of more advanced examples of the same type, which present such a com 
bination of the large dendritic aperture of Dendritina with the isolated pores oi Pene- 
roplu, as to complete (in my opinion) the proof that no valid distinction can be dr-avm 
between these two types, either from the number, the isolation, the position, or the 
shape of the apertures in the septa. This conclusion will probably become less sur- 
prising than it may at first sight appear to such as are accustomed to the study oi toe 
more constant characters presented by the shells of Mollusca, when it is borne m mm 
that the apertures seem to have no other function than to give passage to threads of 
sarcode; and that it is the general character of the Ehizopod type, for such extensions 
of the substance of the body to be entirely destitute of constancy either as to position 
or number. 4 . 
138. If the foregoing conclusion be admitted, it follows that not merely mus e 
genem Pmdritiim and SpiroUna be relinquished, but that both these forms must be 
regarded as mere varieties ot Pemroplis planatm. From the circumstance that the Pen- 
dritim-tyve is found only in tropical seas, and that it attains a far larger size than the 
ordinary Pemroplis-type, whilst the latter seems to be almost staiwed out (as it were) 
in the Mediterranean,— presenting itself there under its humblest form, and scarcely 
extending itself at all into northern seas,— I am disposed to think that temperatm-e has 
a considerable influence in producing these varieties. I shouU be far, however, from 
attributing the entfre result to this agency alone, since we find Penertplis presentmg 
itself abundantly in tropical seas, along with Pendritina. But as it is in the h' e ter- 
ranean forms that we meet with the extreme of flattening and with the most u^orm 
singleness of the row of pores, whilst it is among the tropical forms that we &rd Paie- 
roplis not merely attaining its greatest dimensions, but also presenting the closest 
approximation to Pendritina in the turgidity of its spire and in the areangement of its 
septal apertures, it seems obvious that the development of this type of structure is 
favoured by a constantly high temperature i and further, that Pe,idritina may be 
regarded as the highest form, towards which PemropUs tends nr proportion as it is 
subjected to that influence.— As I have not had the opportunity of examiiimg the 
fossil forms of this type, I am as yet unable to say how far the foregoing conclusions 
will be borne out by the phenomena which they present. 
Genus Opeeculina. 
139. The collection of Mr. Cuming contains a large number of Nautiloid Forami- 
nifera, ditfering considerably from one another not only in size and proportions, but also 
