OF NORTHUMBERLAND AND DURHAM. 205 
much diminished that it leaves little more than a spot, and in 
that case the species might be taken for the last ; but it may 
always be known from it by the thinness of the general envelope 
and the more variegated reddish colour of the inclosed animals. 
3. B. virescens, Ald. and Hane. 
General envelope moderately thick, olive-brown coloured, 
sprinkled with yellow spots. Individuals forming circles of from 
six to twelve. Colour grass-green, varying to greenish yellow, 
and occasionally to pale grey ; the colour is in most cases con- 
fined to the lower part of the animal, the upper portion being so 
nearly the colour of the envelope as to be with difficulty distin- 
guished from it. Branchial apertures large, with a faint red 
margin ; the tentacular filaments very conspicuous within them, 
of a pale yellowish colour. When magnified, the colour of the 
body is shown to be formed of a copious sprinkling of opake 
spots, mostly confined, as before stated, to the lower part of the 
animal, but sometimes extending round the disc. Common cen- 
tral apertures largish, margined with red. 
Not uncommon on the under side of stones within tide-marks, 
along with the last. The arrangement of the markings distin- 
guishes it from the B. smaragdus of Milne Edwards. 
4, B. potycycius, Sav. ? 
General envelope thin, dull greenish brown. Individuals 
forming circles of from 4 to 9 each, generally of a purplish hue, 
occasioned by a spotting of claret-colour and blue intermixed 
with spots of opake white ; the white usually forming one or two 
large blotches in the centre of the body on a dark blue ground 
and there is also a circle of white, or sometimes reddish, spots 
round the disc. General apertures rather small; the edges 
thickly sprinkled with white and blue. 
Botryllus polycyclus, Forb. and Hanl. Brit. Moll. i. 21. 
On the under side of stones within tide-marks, not rare, but 
less frequent than the three preceding. 
d. B. castangus, Ald. and Hane. 
General envelope very thin and pellucid, with a few scattered 
brown marks and black punctures on the margin. Individuals 
large, placed in irregular circles of from 6 to 8, of a chesnut 
