Pvn H,i I'UitlS

280 CARDIID.E.
ling) couldn't get out. Another habit, however, which
this little cockle possesses, is more remarkable. In the
'
Antologia di Scienze natural!/ published at Naples in
1841, Sr. Costa described and figured a shell under the
name of C. parasitum, which appears to be a variety
of C. exiguum. He observes that it attaches itself by
means of a byssus to the boughs of trees laid down in
the sea for the purpose of collecting oyster-spawn. A
short account of these nurseries has been given in p. 46
of the present volume. Some interesting particulars of
the embryogeny of C. exiguum will be found in the
treatise of Professor Loven on the development of the
Acephala Lamellibranchiata,
to which I have elsewhere
referred. The decided angularity of the shell serves as
an unfailing test to recognize this species, although (like
its congeners) it is subject to considerable variation in
respect of shape and colour. In the fry
the dorsal mar-
gin is straight, making the outline more square than
triangular.
Gmelin constituted this species from a figure in
Lister's c Historia Conchyliorum/ t. 317. f. 154 (" A.
Pectunculus exiguus, subfuscus "), which unquestionably
represents our shell. His own description is slight ; but
in adopting the name originally given by Lister he has
been followed by all conchologists except Donovan and
the authors of the * British Mollusca/ who have called it
pygmcenm. Among other synonyms (for variatal forms)
may be mentioned C. subangulatum of Scacchi, C. Siculum
of Sower by, C. stellatum of Reeve, and C. aquUinum of
Mittre*. C. parvum of Philippi appears
to be also a
variety, and C. muricatulum of Montagu (from Walker,
pi. iii. f. 83, 84) the fry of the present species.