Pvn H,i I'UitlS

ARCA. 169
ventral spines of certain Echinoderms. Living specimens
of P. glycymeris, which I have dredged in 85
fathoms, had their shells beautifully marked by varie-
gated streaks of a bright reddish-brown.
Mr. Searles Wood has taken a great deal of pains in
making out the synonymy of this variable species
in a
recent and fossil state. He cites no less than eighteen
different names. Among the best-known of these are
Area pilosa (Linne), A. bimaculata (Poli), Pectuncidus
stellatus (Lamarck), P. undatus, decussatus, and num-
marius (Turton, but not Linnets species of Area bearing
these names), and P. lineatus (Philippi). The Area
minima of Turton' s '
mitted by him,
in his '
Conchological Dictionary '
Dithyra/ to be the fry
was ad-
of this
referred it to A.
species, although Leach subsequently
Noes. Mr. Hanlev at first asserted that, from an exa-
mination of Linnets own specimens, his A. glycymeris
was the P." violascens" (violas cescens) of Lamarck ; but
he afterwards corrected the mistake. The first localitv
given by Linne (on the authority of Lister) for A. glycymeris
was " Garnsey," where P. violascescens has never
been found. The last-named species appears to be his
A. nummaria, judging from the description
tema Naturae/
in the (
Genus V. ARCA*, Linne. PL IV. f. 5.
Sys-
Body oblong and thick : mantle entirely open, except at the
back, in some species fringed
furnished (as in Pectuncidus) with ocelli :
with tentacular filaments, or
foot large and ex-
tensile : byssus composed of glutinous threads, which sometimes
form a compact mass, or plug of attachment.
Shell oblong or rhomboidal, gibbous, inequilateral, and in
a few species slightly inequivalve : epidermis fibrous : ligament
* A chest ;
or from the supposed resemblance of Noah's ark to this shell.
I