Pvn H,i I'UitlS

MODIOLARIA. 127
Yar. 2. semilcevis. Shell narrower, yellowish-horncolonr; ribs
on the posterior area slight and scarcely perceptible, L. 0*1 7-5.
B. 0-1.
Habitat : Gregarious at the roots of seaweeds (especially
Corallina officinalis) between tide-marks, and in
the Laminarian zone everywhere from Shetland to the
the Channel Isles. Var. 1. Southampton (J. G. J.) ;
estuary of the Orwell, Suffolk (Clarke). Var. 2. Staffa
(Alder). Some specimens from Lismore near Oban
also have no trace of ribs on the upper part of the pos-
terior area. Having had an opportunity of carefully
examining and comparing an extensive series of specimens
of Modiola laevigata, Gray, and the variety sub-
striata, from different parts of the Arctic seas, I am convinced
that they are not distinct from the present species.
The gradual passage from any one of these forms
to another is very evident, if a sufficient number ol
examples of all ages and from many localities are submitted
to the inspection of a tolerably practised ob-
server; and the deplorable fashion of species-making
might be in some measure restrained by adopting this
method in all cases, instead of selecting a few particular
specimens and discarding young shells and those
which offer inconvenient proofs of transition. As an
upper tertiary fossil the variety laevigata
has been found
at Elie in Fifeshire by the Rev. Thomas Brown, and the
typical
form occurs in the mammalian bed at Chilles-
ford. It has a wide extra- British range, from North
Greenland and New England to the iEgean.
This little creature is a very industrious seamstress ;
for Mr. Alder says it " forms for itself a kind of nest or
case by stitching together the small seaweeds or coral-
lines with its byssal threads." Forbes and M'Andrew
dredged it at a depth of 30 fathoms in the Irish Sea, off