156
.
G. H. PARKER
_
and are apparently characteristic not only for species but
'
groups of gastropods.
In the majority of species thus
'
'
'
fai‘ examined, the pedal waves course forward over the foot, thus
_’
.
agreeing in direction with the animal’s locomotion.
Vlès has
_
'
_
appr0priately designated this type of movement as the direct type
'
‘
and has given the following gastropods as examples; the pulmo'
.
nates (including Onchidium), Aplysia, Aeolis, Doris, Hahot1s,
_
'
Trochus, Cyclostoma,' and certain small species of Littorina.
I
_
can conrm this statement for such of these molluscs as I have
'
examined, namely, many pulmonates, including Onchidium, and
=
|
I can add to this list Crepidula fornicata.
In other gastropods
-
the waves pass over the foot from anterior to posterior and this
}
”
,
.
been designated by Vlés as rctrogmde. As examples he
'
has givenAcanthochites fascicularis, Littorina littorea, and L. 9
mdis.
Besides conrming Vlès’ observation on Littorina ht—
—
torea, I can add to this list Dolabrifera virens Verrill, Tectarius
‘
-__'nodulosus Gmel., Nerita tessellata Gmel., and Chiton tuber—
‘_
culatus. Linn, According to the observations of Jordan (’01,
”_”;l
p.. 99)…Aplysia belongs under this head and not under that of
'
‘
direct. type as given by Vies.
'
;
;
'
In both chief types of movement several- subtypes can be dls—
tinguished
as
the lateral extent of the pedal waves
_
In some _gastropods .ea—Ch…vvave extends over the functional Width
of the” foot" and thus
by only a s1ngleserles
—
'
of_ waves.__ This,subtype has been termed by Vlès monotamC,
.;and is exerhplied by the, 'jpu1monàtes 'i‘and; chitons. Inaddition
.
v
_
to these
a monOtax1C
_
'
-
waVe,-‘ _In
other gastropods the
or even struc—
;
'
«tural_ly dw1dedalengthe median planeandexh1b1tsa dauble@ys
’
île—m OÎWWGS°Œ%tandtheothelleTh1ssubtypehasb%n
'
,