120 NUDIBRANCHIATA.—TRITONIADA. 
but is considered somewhat rare. It seems to be 
a deep water species: I have procured it by trawling 
off Portland. It is remarkable for a power pos- 
sessed only in a very limited degree by any of the 
Mollusca, that of producing an audible sound. 
Professor Grant, to whom we are indebted for 
a record of the curious fact, says “that the sounds 
resemble very much the clink of a steel wire on 
the side of the jar, one stroke only being given at 
a time, and repeated at intervals of a minute or 
two. When placed in a large basin of water, the 
sound is much obscured, and is like that of a watch, 
one stroke being repeated as before at intervals. 
The sound is longest and oftenest repeated when 
the Tritonie are lively and moving about, and is 
not heard when they are cold and without any 
motion. Inthe dark, [have not observed any light 
emitted at the time of the stroke; no globule of air 
escapes to the surface of the water, nor is any ripple 
produced on the surface at the instant of the stroke. 
The sound, when in a glass vessel, is mellow and 
distinct.” 
The Professor has kept these Tritoniw alive in 
his room for a month; and during the whole period 
of their confinement, they have continued to pro- 
duce the sounds, with very little diminution of 
their original intensity. In a still apartment, they 
are audible at the distance of twelve feet. ‘“ The 
sounds obviously proceed from the mouth of the 
animal, and at the instant of the stroke we observe 
the lips suddenly separate, as if to allow the water 
to rush into a small vacuum formed within. 
As these animals are hermaphrodites, requiring 
mutual impregnation, the sounds may possibly be 
a means of communication between them; or if 
