UARDIOLA- DIMYARIA. O7 
equivalve, and besides having two cardinal teeth, there are remote lateral 
teeth on each side of the beaks. 
The Carditez inhabit the ocean, and fossil species are met with in the newer 
beds above the Chalk, the Crag, Calcaire-grossier, and London Clay. 
Genus XIX. — CARDIUM. — Linnaeus. 
Generic Character. — Shell equivalve, nearly equilateral, 
and more or less gaping posteriorly ; generally with strong 
ribs radiating from the umbones to the margins; inside of 
the lips crenulated, or dentated, corresponding in size to the 
ribs ; two approximate oblique cardinal teeth in both valves, 
locking into each other cross-ways ; and with two remote 
lateral teeth in both valves; two lateral distinct muscular 
impressions in each valve ; mantle impressions entire ; liga- 
ment external. 
Cardium Parkinsoni. Plate VIII. fig. 21. 
For the most part, there is a slight difference in the form of the two valves 
of the Cardize, and in some few instances the external surface is smooth, and 
destitute of ribs, but they have invariably a toothed or crenulated internal 
margin, the crenulations being always small in the smooth species. Although 
a very natural genus, there is nevertheless considerable variety in external 
form: the C. twberculatum is almost globular ; some are considerably longitu- 
dinal as C. soleniforme, and others are deeper than wide as C. biradiatum, and 
the C. Cardissa has its sides considerably compressed. 
The Cardie inhabit the ocean, generally lurking in the sand near low- 
water-mark. Fossil species are met with in nearly almost the whole fossil- 
iferous series, from the Mountain Limestone upwards; and are very numerous 
in the newer formations, such as the English Crag, London Clay, and Green- 
sand, 
Genus XX. — HIPPOCARDIA. — Brown. 
Generic Character. — Shell transversely elongated; hinge 
line long, rectilinear ; anterior side with a short prolonga- 
tion; posterior side lengthened into an acute, wing-shaped 
auricular process; generally longitudinally ribbed ; beaks 
but slightly produced. 
Hippocardia Hibernica. Plate VIEI. fig. 10. 
Found only in a fossil state in the Mountain Limestone. 
We have instituted this genus for the reception of several remarkable fossils, 
which are met with in the Mountain Limestone. The type of the genus is 
the Cardium Hibernicum of Sowerby. 
Genus XXI.— CARDIOLA.— Broderip. 
Generic Character. — Shell equivalve, oblique, inequila- 
teral ; beaks prominent and curved ; surface concentrically 
furrowed ; hinge line long, with a flat area. 
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