30 
DB. CABPBNTEE’S BESEABCHES ON THE EOBAMINIEEBA. 
of the injury, in a narrowing of that part of the convolution which succeeds it, the new 
chambers being formed as it were on the contracted basis to which their predecessors have 
been reduced. A very remarkable feature in all these reparations is the continuation of 
the marqinal cord along the fractured edge. It might have been supposed to the wound 
would have been healed with some rude exudation, which would have given nse to an 
amorphous shell-structure ; but instead of this, we find the reparation chiefly effected by 
a new production (probably by extension from the old) of that portion winch gives the 
most evidence in its canalicular structure of being intimately connected with the vital 
changes taking place in the organism. This phenomenon is beautifully displayed m the 
specimen represented in fig. 4, Plate VI., which exhibits another remarkable feature for 
which it is difficult to account, -a reversal in the dhection of growth which has fcien 
place after the fracture. Although the specimen is unfortunately not complete, there 
can be (I think) no reasonable doubt that its convolutions must have taken the coui'se 
indicated by the dotted lines; and it would seem that after the first two convolutions 
had been formed, the spire had been broken across, almost through its centre. It wi 
be at once seen, by comparing the direction of the septa of the second convolution wit 
that of all those which surround it, that the latter have been reversed ; and although the 
part in which the reversal actually took place is unfortunately wanting, yet there can be 
little doubt that it was made as indicated in the figure («). But the most curious featm-e 
in the specimen is this,~that the extension {ac) of the marginal cord which has closed m 
the fractured portion has obviously proceeded not from the later (^), but from the earlier 
(c) of the two fractured extremities of the second convolution; and it is in this bac/c- 
ward growth that the reversal would appear to have originated. A somewhat similar 
retrograde increase has been already noticed among the modes in which OrhitoMes is 
occasionally repaired 39) ; and it obviously shows that every portion of the organism 
is equally capable of extending itself when left free to do so. It is worthy of remar , 
that the growth of this specimen subsequently to the injury, has taken place more after 
the plan oiNummulites than on the ordinary plan of Operculina-, the convolutions being 
more numerous than usual, and their rate of increase slow. There is evidence, however, 
in the presence of a small fragment of the final whorl, that it underwent the thuming- 
out which is characteristic of its type. Notwithstanding the great number of specimens 
which I have examined, I have not met with one that presented any such departime 
from the normal type of growth as would deserve to be termed a monstro^ty ; so that it 
would seem as if such aberrations were more frequent in the cyclical than in the helical 
type. 
Genus Amphistegina. 
164. History.— Ttih genus was first constituted by M. d’Okbisny m 1825, for the 
reception of a type of Foraminiferous shells which does not seem to have been prevrously 
noticed by those who have given their attention to this group, in consequence, it may 
be of its limitation to the seas of warm latitudes. Notwithstandmg the very close ito 
tio’nship which, as I shall presently show, it bears to Wmnmulites and other Nautiloid 
