ORDOVICIAN BIVALVE BIOGEOGRAPHY 41were included in the Palaeoheterodonta by Cox
etal (1969).
The actinodontid heteroconchs include forms
with a sheaf of ventrally radiating teeth. The first
such form to be described was Actinodonta
cuneata Phillips, 1848, from the Middle Llan-
dovery (Aeronian) of South Wales. Pojeta
(1971) wrongly recorded this species as from the
Ordovician and a number of other authors have
reported the genus from the Ordovician. For
example Barrois (1891) figured several bivalves
from the Gres Armoricain that he attributed to
Actinodonta, and Babin (1966) also attributed
some Armorican forms to the genus. The
lectotype of A. cuneata was designated by
Stubblefield (1938) and a latex cast of this speci-
men was figured by Pojeta (1978). The teeth
branch out subumbonally and several of the
posterior teeth are elongated. It has now
become clear that Actinodonta is confined to the
Silurian and that Ordovician forms ascribed to
that genus will need new names. Within the
Lower Ordovician, the genus Carminodonta
Cope, 1996b approaches Actinodonta the closest
in dentition; the former is only known from the
Lower Arenig of the Llangynog Inlier, South
Wales. Other actinodontids with this type of
dentition include the Mid-Ordovician genus
Copidens Pojeta & Gilbert-Tomlinson, 1977
from the Georgina Basin of Australia; this
species was also recorded from South China by
Guo (1988) as a new genus and species,
Zadimerodia fastigata, but the two forms are
clearly conspecific (Fang & Cope, unpublished
work). Ananterodonta Babin & Gutierrez-
Marco, 1985 from the Lower Llanvirn of Spain,
is a further actinodont of this type; this is still
known only from a single specimen. The earliest
Cycloconcha was recorded from the Middle
Ordovician of Argentina by Sanchez (1986) but
is subsequently known from Laurentia. Late
Ordovician species of Cycloconcha show the
typical actinodont subumbonal multiplicity of
teeth; such a form is the C. mediocardinalis
Miller, 1874, figured by Pojeta & Runnegar
(1985, fig. 13A).
Heteroconchs with reduced dentition are
more widely dispersed. The family Redoniidae
Babin, 1966 comprises heteroconchs with much
reduced subumbonal teeth and lacking anterior
dentition. Redonia itself has a wide distribution,
being recorded from the Lower Arenig of the
Montagne Noire (Babin 1982a) and Morocco
(Babin & Destombes 1992). The genus was also
recorded from the lowest Middle Arenig of
Argentina (Sanchez & Babin 1994; Sanchez
1997b). It occurs in the Upper Arenig of the
Welsh Borderland (Cope 1999) and Turkey
(Dean & Monod 1970) and in the Llanvirn of
Morocco (Babin & Destombes 1992) and
Bohemia (Barrande 1881). Other redoniids
include the Avalonian genus Moridunia which is
abundant in the Lower Arenig of South Wales
(Cope 1996b) and probably occurs too in the
poorly preserved Ramsey Island fauna (Hicks
1873), whence it was recorded as an Actinodonta
(Carter 1971). In Spain another local genus is
found in the Llanvirn, Dulcineia Babin &
Gutierrez Marco, 1991, that is characterized by
crenulate teeth. Redoniids appear to be charac-
teristic of high to median latitudes as no member
of the family has yet been found in any of the low
latitude areas.
Another group with very much reduced
dentition, frequently related in the past to the
heteroconchs, is the family Modiomorphidae.
Pojeta (1971, p. 20) remarked upon the vague
concept of this taxon and the fact that it prob-
ably included more than one family level group.
Recent work has confirmed this view (Fang &
Morris 1997), and it now seems that there are
two separate bivalve groups involved, neither of
which should be assigned to the heteroconchs.
These are discussed more fully below.
The genus Babinka Barrande, 1881 is one of
the most perplexing of Ordovician bivalves as
far as its affinities are concerned. Its multiple
muscle scars suggested that it was closely related
to monoplacophorans to McAlester (1965, 1966)
who decided that it was an early lucinoid.
Starobogatov (1971) disagreed with McAlester's
orientation of Babinka and thus its suggested
affinities, but Pojeta (1978) agreed with the
orientation and systematic placing. Other
workers, however (e.g. Babin 1982a; Cope
19976), have preferred to regard it as a hetero-
conch. More recently, Taylor & Glover (2000)
have described the anterior respiratory pouch in
the lucinoids; this is apparently absent in
Babinka and Taylor & Glover (2000, p. 221)
concluded that McAlester (1965) had exagger-
ated the lucinoid characters of the genus. The
stratigraphical and biogeographical range of
Babinka is also interesting. The earliest
examples are from the Tremadoc of the
Montagne Noire (Babin 1982a), but the genus is
known from the Lower Arenig of Morocco
(Babin & Destombes 1982), from the Upper
Arenig of South Wales (Cope 19976), the Lower
Llanvirn of the Welsh Borderland (Cope 1999)
and Sweden (Soot-Ryen 1969) and the Llanvirn
of Bohemia (Barrande 1881). The genus is thus
widely dispersed over the high to mid-latitudes
of Gondwana and Avalonia and was one of the
first bivalves to reach Baltica.
Babinka is far from the only Ordovician