ORDER III TELEODESMACEA 415 
Family 31. Weneridae. Leach. 
Valves equal, free, closed, with prosogyrous beaks, variably sculptured, with the 
margins more or less dentate, except in the smooth species; adductor scars peripheral, 
pedal distant ; pallial sinus more or less sinuated, arew very distinct ; resiliwm usually 
external, embraced by the ligament ; hinge plate developed ; formula of the cardinals 
uae with a single obsolete lateral in one valve; the cardinals frequently bifid, 
usually radially disposed and sub-equal in size, except the posterior left one, which is often 
obsolete or obscure; supplementary cardinals or 
rugosities are present in specialised forms. Jura 
to Recent ; maximum in Tertiary and later. 
The family must be divided into at least four 
sub-families, as follows :— 
a. Venerinae: typical, with produced siphons, 
not byssiferous, the young not retained within the 
mother after leaving the egg. 
b. Cirecinae : with separate short siphons, correla- 
tive nearly simple parallel line, sub - internal, 
partially amphidetic resilium, and compressed beaks. 
c. Tapetinae: with long but partly separated 
siphons, a byssus present at least in the young ; 
hinge with no lateral teeth, otherwise like the 
Venerinae. 
d. Gemminae: minute shells, with more or less 
separated siphons, no byssus, obsolete lateral laminae, 
and sheltering the nepionic young within the cavity 
of the mother. 

a. Pronoélla, Fisch. (Pronoé, Ag. non Gueér. 
Mén.) Compressed, pallial sinus very shallow ; 
a posterior lateral and three cardinals in each 
valve. Jura. 
Cyprimeria, Cony. (Fig. 758). Like the preceding, but the right valve with only 
two cardinals, the hinder one bifid ; pallial sinus very shallow. Cretaceous. 
Dosinia, Scop. (Artemis, auct.) Orbicular, lentiform, concentrically sculptured, 
with a deep, well-marked 
lunule; cardinals 3 : 3; pallial 
sinus deep, ascending, pointed. 
Cretaceous to Recent. 
Cyclina, Desh. Cretaceous 
to Recent.  Sumnetta, Link 
(Meroé, Schum.) ; Grateloupia, 
Desm. Tertiary and Recent. 
Venus, Linn. (Fig. 759). 
Oval or rounded, plump, 
cordate, thick ; concentrically 
or radially sculptured, with 
denticulate margins; hinge 
plate broad, with three 
~cardinals in each valve and no lateral teeth; pallial sinus short, angular. Jura 
to Recent; represented by about 200 fossil and as many recent species. Very 
numerous sub-divisions have been proposed; Venus s. s. is typified by V. mercenaria, 
Lam. 
Meretriz, Lam. (Cytherea, auct.), (Figs. 760, 761). Hinge with lateral teeth. 
Tertiary and Recent. 
Fic. 758. 
Cyprimeria discus, Math. sp. Upper Cre- 
taceous ; Gosau Valley, Austria. 

Venus cincta, Eichw. Miocene; Gainfahrn, near Vienna. 
