80 Mr. H. J. Carter on Freshwater Rhizopoda 
part, the anterior half being rather contracted, and the aperture 
large and circular, or slightly elongated transversely. The latter 
feature, together with the tendency of the aperture to an ex- 
centric or terminal position and the depression of the test ante- 
riorly, while it is elevated behind, causes this Rhizopod to bear 
a similar relation to Difflugia that the pleurostomatal form of 
Luglypha (Trinema acinus, Duj., Euglypha pleurostoma, Cart.) 
bears to the latter genus; and when we observe that its test is 
formed of grains of hyaline quartz, and that the pseudopodia 
are digital and obtuse, the alliance is still greater. . The spines 
then become the chief distinguishing character, out of which, 
according to Claparéde and Lachmann (p. 447), delicate pseudo- 
podal prolongations are projected. But even the spines vary 
greatly in number and position (i, d), while in some varie- 
ties they are altogether absent (g,h), as may be seen by the 
group of figures I have given of them, which, being all drawn 
upon the same scale, show not only their relative sizes to each 
other, but to those of the other Difflugie. 
In the lateral view of the large specimen (d), I have endea- 
voured to give another variety in the disposition of the spines, 
and have figured on the test the regular arrangement of short 
straight filaments (e) which, at Bombay, I found occasionally 
substituted for the grains of quartz; while in other instances the 
test was composed of a mixture of both, and sometimes of the 
frustules of Navicula pusilla (mihi) only, with the endochrome 
still in them. Thus, as we have now seen, these animals avail 
themselves of much variety in the material of their covering, 
although grains of sand, and especially of colourless hyaline 
quartz, seem to be preferred. 
ARcELLA, Ehr. 
Arcella'vulgaris, Khr. Pl. II. fig. 14. 
Among the figured specimens of this Rhizopod and its varie- 
ties are the largest that I have seen; and in the horizontal view 
of the depressed form will be observed the double nucleus, viz. 
one situated diametrically opposite the other. This occurs also 
in all the varieties; and I wonder that no allusion has been 
made to the circumstance by other authors who have written on 
this Rhizopod, especially since my figure illustrating the fact 
was published in 1856 (Annals, ser. 2. vol. xvi. pl. 7. fig. 79). I 
think that I have found specimens with only one nucleus, but 
certainly none with “ twelve or fifteen,” as stated by Auerbach 
and repeated by Claparéde and Lachmann (p. 445). But I 
have figures of specimens, observed in the island of Bombay, 
containing even more than this number of what appear to me 
now to have been “ reproductive cells” analogous to those which 
