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Puka shell jewelry and accessory
C. erosa erosa Linnaeus, 1758
The specimen was collected by Mrs. Couacaud at Grand Bay, Mauritius, exposed on basalt rocks. A similar specimen had been
described by Sowerby as C. caurica var. concava (Thes. Conch., pl. 29 (320), figs. 318-319), from Owen's collection.
The C. erosa erosa Linnaeus, 1758, is not melanistic but is considerably rostrate; this had also been collected by Mrs.
Couacaud at Mauritius.
Dr. Schilder, who had the opportunity to view the photographs, commented as follows (in litt.): "The rostration of the shells
is not absolutely the same as that of New Caledonian cowries. The features of C. erosa may be comparable to those from New
Caledonia, though details are aberrant, especially the thickening of the posterior quarter and the total absence of melanism;
the cause of malformation may thus be different. The C. caurica shows quite peculiar features, e.g. total reduction of the
teeth and abnormal dilatation of the aperture in front, features which recall C. tortirostris."
Rostration does not necessarily have to be combined with melanism; specimens of C. clandestina and C. lynx which I collected
in New Caledonia were rostrate but not melanistic; a C. caurica collected at the Bay du Mondoure, was both rostrate and
melanistic, with a grossly dilated anterior aperture.
In land snails real sinistrality is frequent: there are families, genera, and species in which all shells are sinistral. In
some usually dextral species hereditary mutation in a population caused sinistrality of a local race: so all specimens of
Fruticicola lantzi are sinistral in one valley east of Alma Ata while this species is dextral in all other places of Central
Asia. (Schilder 1952, Biotaxonomie (Jena), p. 74, map fig. 36). In other cases, sinistral shells may be classified as rare
abnormalities: so in Helix pomatia, a large edible snail sold in large quantities chiefly in France, there is one sinistral
specimen (called "king") among 6,000 to 8,000 shells, and in the allied smaller species of Cepaea there is one sinistral
shell among 30,000 to 150,000 dextral ones (Schilder 1953, Die Banderschnecken (Jena), p. 17).
In marine gastropods sinistral shells seem to be rarer. A normally sinistral cone (Conus adversarius) from the Pliocene beds
of Florida, has been figured in the Sean Raynon Sabado (n.s.) 2:3 (February, 1960).
In cowries sinistral specimens are extremely rare, if indeed they occur at all. Among the more than 150,000 cowries which the
writer has examined personally during forty-four years special study, there was no sinistral shell. But R. J. Griffiths
(1962, Mem. Nat. Mus. Melbourne, 25:217) mentions a sinistral Notocypraea declivis which is preserved in the South Australian
Museum: its curator would oblige many malacologists if he would publish an enlarged photograph, at least of the basal view of
this curiosity.
Another case of sinistrality in cowries has been proved to be erroneous: Stoliczka (1867, Palaeont. Indica (5) 2:56, pl. 4,
fig. 6) has established a Cypraea anomala from the Cretaceous of India, believing it to be a sinistral shell. But details of
the drawing of the incomplete shell undoubtedly show that Stoliczka's specimen represents its posterior extremity, and not
its anterior extremity as the author supposed, so that anomala is a normally dextral Palaeocypraea (Schilder 1926, Rec. Geol.
Surv. India 58(4):372).
Collectors should be eager to find a really sinistral cowry among the shells which go through their hands, and if they were
happy enough to detect one, they should publish it in the Sean Raynon Sabado, accompanied by a photograph. For such a shell
would be more valuable than the rarest cowry species we know.
But I think that nobody will find a sinistral cowry.
Three small oblong cowries which have been dredged as dead shells in 80 fathoms off the Bonin Islands, have been described as
Erosaria cernica ogasawarensis Schilder 1944 (Arkiv for Zoologi 36.A.2, p. 22); their formulae i.e. length in mm., breadth
in per cent of length (in brackets [parentheses]), and number of labial and true columellar teeth (separated by a colon) are
as follows:
13(60)18:14 (a rather worn paratype), 15(57)17:15 (holotype according to Schilder 1958, Arch. Mollusk. 87:172), 16(56)19:18
(paratype in coll. Schilder No. 7433).
As these shells never have been figured before, I think it useful to publish a photograph of the last-named paratype of 16mm
because a specimen from the Bonin Is. figured by Cate (1960, Veliger 3, pl. 1, fig. 5) is a much larger and broader shell, as
its formula is 29(64)23:24.
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