SPHjEROMA. 
245 
Sphjsroma serratum, Fabr. sp. Serrated Sea Till-ball. 
(Plate XIII. fig. 6.) — Body smooth; tail very smooth, 
obliquely truncated on each side, the lamellae elliptical, 
sharp, the outer serrated externally. 
Of an ashy colour, or whitish marbled with red. 
Rocky shores ; very common. 
Sphaeroma rugtcatjda, Leach. Rough-tailed Sea Till - 
ball . — Body smooth ; tail rough, with its lamellae rounded, 
the outer scarcely toothed externally. Body ash-coloured, 
lineated, and spotted with black. 
Island of Ulva; w T here it was found by Dr. Leach. Ber- 
wick-upon-Tweed (Dr. Johnston). 
Sph^roma Hookeri, Leach. — Body smooth ; the last 
joint of the tail furnished with two oblong tubercles. Ash- 
coloured or reddish, with minute black punctures. 
Coast of Suffolk, whence it was sent by Sir Wm. Jackson 
Hooker to Dr. Leach. The Rev. Alfred Norman finds it 
at Clevedon and in Guernsey. 
There are other recorded British species, but they are 
but imperfectly characterized. 
