Still playing.  And speaking of Houbrick, _Living Fossils_, living fossils,
_The Southern Synthesis_, and the Cerithioidea, there's the family
Diastomatidae, "once widespread in shallow Tertiary seas" but "today
represented by a single extant species Diastoma melanoides, living in sandy
seagrass habitats along the southeastern coast of Australia."  Reaching
30-50 mm, these elongate, turreted shells have a bristly periostracum and
lots of anatomical features that Houbrick found to qualify them as
sufficiently different to warrant single-species family status.

Then there is the order Trigonioidea, containing only a single extant (out
of eight known) family Trigoniidae (Bivalvia). In turn, Trigoniidae today
contains but a single genus, Neotrigonia, which has just six species, all
from Australia. Approximately 20 genera (extinct) are recognized, though all
but Neotrigonia's ancestor, Eotrigonia, had vanished from the rocks by the
early Cenozoic, apparently done in by the same catastrophic factor that
caused the mass extinctions of the late Cretaceous.

For those of you who don't know the pretty little prickly-ribbed,
cockle-like Australian bivalves, they are (I think!) the single marine
bivalves with a nacreous interior.  And they are most closely related to the
Unionoidea, comprising, between the two of the superfamilies, the entire
(debatable)subclass Palaeoheterodonta. The best place to see a bunch of them
(five of the six species) is Kev Lamprell and Thora Whitehead's  1992
_Bivalves of Australia Volume 1_.  Known species:  N. margaritacea (Lamarck,
1804), N. bednalli (Verco, 1907), N. lamarcki (Gray, 1838), N. gemma
Iredale, 1924, N. uniophora (Gray, 1847) and N. kaiyomarumae Habe and
Nomoto, 1976.  The latter is known from a single specimen from off Western
Australia.   (sources are again  _The Southern Synthesis_ (Thomas A.
Darragh);  and _Living Fossils_ (Steven M. Stanley).

Off to find something else to keep me from working.

Lynn again
Louisville KY
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