Pvn H,i I'UitlS

70 pectinidjE.
consists of numerous fine ribs, which radiate from the beaks to
the front and side margins, and have their crests thickly set
with short vaulted spines or prickles ; besides these riblets, the
surface is closely covered with extremely minute and irregular
longitudinal striae, which are raised and divaricate or become
forked, but they are never reticulated or punctured as in
P. Tested. The .colour is of a more sombre hue. The left ear
of the upper valve hangs down much lower, and is nearly
entire instead of being deeply notched as in that species ;
the byssal sinus is consequently larger. L. 0-725. B. 0*7.
and
Habitat : Seas of Shetland, Scotland, north-eastern
coasts of England, north, east, south, and west of Ire-
land, Isle of Man, and Scilly, in 12-90 fathoms, hard
ground. Morch has procured it from the Faroe Isles,
and Danielssen from West Finmark. It also inhabits
other parts of the Scandinavian coast. M fAndrew has
dredged it in Vigo Bay at a depth of 15 fathoms, and
describes it as a Calabrian fossil under the
Philippi
name of P. rhnulosus.
The shell is sometimes distorted. The pallial ocelli or
eyelets are of unequal size and irregularly placed ; they
gleam with an opaline lustre. Living specimens which
I dredged in 85 fathoms had the shells highly coloured
and streaked. Mr. Norman has noticed,
in his list of
Clyde Mollusca, that the shells of this species lose the
azure-blue colour after being kept in a closed cabinet.
This is remarkable, because certain colours of shells and
other animals {e.g. pink and reddish- brown) fade, and
even vanish, unless the light
is excluded. In the British
Museum it has been found necessary to replace, every
two or three years, fresh specimens of many delicate-
tinted butterflies exposed in the show-cases; and in
the museum at Amsterdam the shells are always kept
covered to prevent loss of colour. P. striatus attains a
greater size than P. Testes. My largest specimen is about