124 NUDIBRANCHIATA.—EOLIDID A. 
GENUS HOLIS. 
A vast number of species are comprised in this 
genus, and nearly fifty have already been discovered 
on our own shores. Their body is somewhat slug- 
like, sometimes broad, but more generally slender 
and much lengthened, without the least trace of a 
mantle. The skin is smooth, and not stiffened with 
spicula; the head is prolonged into two smooth 
tapering tentacles, which are apparently organs of 
touch, being waved about with great vivacity when 
the animal crawls ; besides these there are two dorsal 
tentacles, situated as in Dorzs. Their surface is 
sometimes smooth, but sometimes set with mem- 
branous rings or oblique plates ; the eyes are placed 
behind them. The branchie are lengthened, cylin- 
drical, spindle-shaped, or flattened papillee, arranged 
in transverse rows or clusters along the sides of the 
back, often very numerous. ‘These organs usually 
project outwardly, leaving an open space down the 
middle of the back; they are commonly carried 
inclining backwards, and overlapping each other ; 
but when the animal is alarmed or irritated, and 
particularly when it seizes its prey, they are stif- 
fened, erected, and brought forward like tlie quills 
of a porcupine. 
All the species are carnivorous, fierce, and vora- 
cious; some prey upon their weaker fellows, and 
even devour their own spawn. ‘The ordinary food 
of most of the species appears to be the various 
kinds of zoophytes; some of the minuter sorts, 
creatures of great beauty, are almost invariably 
found nestling in the tiny shrubs of Sertularians, 
and there can be no doubt that they devour the 
polypes. Mr. Alder has seen /. coronata feed upon 
