PROGRESS OF MICROSCOPICAL SCIENCE. 
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height, 6 inches in diameter at the top, and about 2 inches at the 
base. It is perfectly formed, and the base bears the distinct im- 
pression of the cable, and a few fibres of the coir rope used as a 
sheath for the telegraphic wire still adhering to it. As the cable has 
been laid only four years, it is evident that this specimen must have 
grown to its present height in that time, which seems to prove that 
the growth of coral is much more rapid than has been supposed. 
Remarlcs on the Rhizopod Genus Nebela. — In the ‘ Proceedings of 
the Academy of Natural Sciences of Philadelphia,’ it says that at a 
late meeting Professor Leidy stated that in order to facilitate a ready 
reference to ordinary forms of rhizopods, he was disposed with some 
other observers to restrict the genus Difflugia to those rhizopods with 
lobose pseudopods, which ordinarily possess a covering or test com- 
posed of extraneous bodies, such as particles of quartzose sand, and 
diatom cases. In the genus Nebela, which he had viewed as distinct 
from Diffiugia, the test is composed of discoid plates and minute rods, 
apparently siliceous and intrinsic to the structure of the animal. To 
the genus Nebela probably belong the species named by Ehrenberg, 
Difflugia collaris, D. cancellata, D. carpio, D. binodis, D. annulata, and 
D. laxa. Likewise the Difflugia peltigeracca of Carter, most of the 
forms described by Wallich under the name of Difflugia pyriformis, 
var. symmetrica, and also the Difflugia carinata of Archer. Formerly 
Professor Leidy had indicated several species under the names of 
Nebela ansata, N. equi-calceus, N. sphagni, N. numata, N. barbata, and 
N. flabellulum. ‘ Pr. A. N .S.,’ 1874, 156. Most of the above-named 
species of Ehrenberg had been referred by the same author to a group 
with the names of Reticella and Allodictya, headed with a species 
named Difflugia asterophora, which, so far as could be judged from the 
description and figure, did not coincide with the characters of Nebela. 
Of the forms referred to Difflugia symmetrica by Dr. Wallich, the first 
one described has recently, by Schultze, been viewed separately from 
the others as characteristic of a new genus with the name of Quadrula 
symmetrica. The test of this is composed of quadrate plates, arranged 
in rows, like bricks in a wall. In all the species referred to Nebela, 
which have been observed by Professor Leidy, in all instances the 
test is compressed pyriform. Wallich remarks in reference to the 
tests of Difflugia symmetrica, that they “ are sometimes so compressed 
as to give the aperture the undulating appearance represented in 
figs. 27, 29 and 30, but more frequently the tests are not compressed, 
and the aperture presents the ordinary circular or nearly circular 
outline.” The species Nebela numata, probably synonymous with 
D. collaris, is an exceedingly abundant form, in much variety in our 
sphagnum swamps, and illustrates well the character of the genus, 
and also exemplifies the extraordinary variation in the structure of 
the test, which appears to be common also in the other species of 
Nebela. In some individuals of Nebela numata, the test is composed 
of or invested with comparatively large circular disks of uniform 
size. In other individuals the disks are of the same character, 
but oval. In other individuals again the test is invested with 
circular or oval disks as in the former, but separated, uniformly 
