REPORT ON THE FORAMINIFERA. 
703 
exception being Rotalia ammoniformis, an outspread modification of tlie type in which 
the later whorls are somewhat evolute, that is to say, so far non-embracing as to leave a 
portion of the earlier convolutions visible on the inferior side. 
The umbilicus is sometimes depressed or deeply excavated, but more frequently it is 
filled with a deposit of clear shell-substance. The aperture of the test, typically, resembles 
that of the other Rotaline genera — a simple curved chink or fissure on the inferior face of the 
terminal segment, close to the line of union with the previous convolution, and is usually 
placed nearer the peripheral than the umbilical margin. The exterior of the test is either 
entirely smooth (. Rotalia soldanii), or smooth above and granular beneath (Rotalia 
beccarii) ; or the sutures are marked externally by raised bands or rows of exogenous 
beads (Rotalia ornata ) ; or, lastly, in rare instances the surface of the shell is ornamented 
with a network of embossed lines (Rotalia clathrata). 
The most striking deviation from the normal Rotaline contour occurs in certain 
species, the tests of which have calcarate or rowelled margins. This condition is 
produced in two different ways, — either the peripheral ends of the chambers are drawn 
out so as to form points or projecting angles (Rotalia calcar ) ; or else three or four long 
spines are thrown out by the septa of the first whorl of chambers, and diverge radially 
from the periphery of the test (Rotalia pulchellci). 
A somewhat anomalous modification of the typical structure, resembling the “ Asteri- 
gerine ” varieties of Discorbina, presents itself in Rotalia carinata and Rotalia lobata , 1 
two forms in which “ the umbilical lobes of the chambers are separated from the principals 
by the intervention of a septum, so as to constitute a secondary series of chamberlets, 
which interdigitate or dovetail themselves between the proper chambers, as do those of 
the lower surface of Amphistegina vulgaris and its varieties, instead of lying in a lower 
plain like the subsidiary chambers formed by astral flaps in Discorbina .” 2 
The microscopic structure of the test of Rotalia exhibits a marked advance on that of 
the allied genera. The walls are of fine texture, and the 1 pores are as minute as those 
of the average of the NummuliniD/E. In many, perhaps in the majority of species, the 
septa are double ; and in some cases a considerable portion of the shell consists of an 
intermediate or supplemental skeleton, furnished with a more or less, complicated canal- 
system, — a feature best illustrated by Rotalia schroeteriana. 
The distribution of the genus may be very briefly indicated. No true Rotalice have 
been found within the Arctic or the Antarctic circle, but the genus is represented by one 
or other of its species in every part of the tropical and temperate zones. It attains its 
highest structural development, and the individual specimens their largest dimensions, in 
the shallow water of warm seas. It inhabits brackish pools and estuaries, is abundant in 
1 Asterigerina carinata, cl’Orbigny, Foram. Cuba, p. 118, pi. v. fig. 25; pi. vi. figs. 1, 2 ; ancl Asterigerina lobata, 
ibid., p. 119, pi. v. figs. 19-21. 
2 Carpenter, Introd. Foram., p. 213. 
