ON THE GENUS POLYMORPHINA. . GEH 
tional cases the varietal distinctions are derived chiefly from such characters as the form 
of the chambers, their number, the degree in which they overlap, the amount of 
depression at the sutures, and the general contour of the shell, as determined by their 
fitting together. 
2nd. Amongst the * ornamented ” varieties may be found almost every description of 
surface-marking known in the simple Foraminifera. The normal hyaline condition of the 
young shell is seldom preserved in the adult, but by degrees the delicate test is thickened 
and rendered opaque from the continued deposit of calcareous matter. This process 
usually takes place with uniformity over the whole surface; and as the pseudopodial per- 
forations continue open, their length is necessarily increased, and from being mere minute 
circular apertures they become tubes traversing the shell-wall. A portion of a thickened 
shell exhibiting this tubular structure is shown at Plate XL. fig. 12, f. 
But in another, large class of cases, the caleareous matter deposited by the sarcode 
issuing through the perforations of the originally thin and smooth chamber-wall, pro- 
duces, by uneven deposition, a series of very different results. The characters depending 
on exogenous growths so formed are sufficiently marked to yield varietal distinctions, 
and we have employed the trivial names which previous authors have given in regard 
to the more salient of them; but it must be understood that in whatever guise the shelly 
outgrowths appear—whether as mere rugosities, as bristles, spines, tubercles, granular 
lines, striæ, or ribs—they all, physiologically speaking, originate in the same way, and, 
as might be expected, pass into each other by insensible degrees. 
In so variable a genus there is perhaps less to be learnt from chance monstrous speci- 
mens than in those whose normal range of modification is narrower; indeed it becomes 
. difficult, with such a group, to say what constitutes a monstrosity. The only really 
anomalous specimens we recollect, setting aside the fistulous or cervicorn varieties, here 
treated of separately, are a few rare examples which are partially double and present 
two principal orifices instead of one. An individual of this sort is represented at 
Plate XXXIX. fig. 1, c. It is of no special interest, except from the analogy it bears to 
the double-growing Lagene and Cristellaria that are occasionally met with. 
Distribution.—The geographical area of the distribution of the genus Polymorphina is 
coextensive with a certain bathymetrical range throughout the world. Its “home” is in 
shallow seas, and it can scarcely be said to flourish at greater depth than 60 or 80 fathoms, 
though occasional specimens are still foúnd at 90 fathoms, and under favourable condi- 
tions it may occur in still deeper water*. In littoral sands, or those dredged in the Lami- 
narian, the Coralline, or the Coral zone, whatever the latitude, some variety of the type 
is sure to be found if Foraminifera are present at all. 
Arctic dredgings off Hunde Island and off the coasts of Greenland and Norway have 
yielded fine specimens. Proceeding southwards, the genus is of common occurrence in 
* At the time this paragraph was written we had not seen Dr. Sars's valüable paper, containing * Additional 
Observations on the Animal Life met with in the Depths of the Sea,” which mentions the occurrence of three varieties 
of Polymorphina, viz. P. lactea (typica), P. compressa, and P. tubulosa (=P. Orbignii of the present memoir), in 
 soundings from 300 fathoms; but as this fact does not affect the general aceuracy of our statement, we have allowed 
it to remain as originally written. 
VOL. XXVII. 2 F 
