BIVALVE Identification

 TO STUDY THE GENERA OF FOSSIL BY THEIR EXTERNAL MORPHOLOGY AND ALSO THEIR STRATIGRAPHIC RANGES:

CARDITA:

Fig:Cardita

1. Shell form: Triangular(Equivalve and equilateral)
2. Umbo: Pointed anteriorly
3. Hinge line: Curved
4. Dentition: Heterodont
5. Adductor impression: Dimyrian , An-isomyrian
6. Pallial line: Prominent,Pallial sinus is also present
7. Ventral margin: Smooth
8. External ornamentation: Concentratic lines are present
9. Special character:  Triangular , shell form is present . The dentition is heterodont . Adductor
impression is dimyrian , anisomyrian . Pallial line and pallial sinus are prominently present .
10. Name of the genus: CARDITA
11. Bio-status: Phyllum - Mollusca
                              Class- Pelecypoda / Bivalve/ Lamellibranchia
                                    Order - Heterodonta
12. Range in time: Triassic-Present
13. Indian horizon: Niniyur formation of cretaceous of trichonopoly

PECTEN:

Fig:Pecten

1. Shell form: Sub circular , equivalve and inequilateral
2. Umbo: Centrally present
3. Hinge line: Straight
4. Dentition: Isodont
5. Adductor impression: poor development of monomyrian
6. Pallial line: Absent
7. Ventral margin: Crenulated
8. External ornamentation: Coarse radial rib,well developed ears
9. Special character: Sub circular shell form with straight hinge line, isodont , coarse radial rib
    and well developed ears.
10. Name of the genus: PECTEN
11. Bio-status: Phyllum - Mollusca
                             Class – Pelecypoda
                                Order - Heterodonta
12. Range in time: Carboniferous to present
13. Indian horizon : Triassic of spiti

ARCA:

Fig:Arca

1. Shell form: Triangular / Quadratrangular ( Equivalve and inequilateral )
2. Umbo: Prominently anterior
3. Hinge line: Straight
4. Dentition: Texodont
5. Adductor impression: Poorly developed dimyrian-isomyrian
6. Pallial line: Pallial line present
7. Ventral margin: Crenulated
8. External ornamentation: Coarse radial ribs and concentratic lines
9. Special character: Shell form is triangular/quadrangular.Hinge line is straight,poorly
developed dimyrian-isomyrian adductor impression.Coarse radial ribs and concentratic line.
10. Name of the genus: ARCA
11. Bio-status: Phyllum-Mollusca
                            Class-Pelecypoda
                                Order-Taxodont
12. Range in time: Jurassic to recent
13. Indian horizon: Cretaceous to trichinopolly

OSTREA:

Fig:Ostrea

1. Shell form: Irregularly circular
2. Umbo: Prominent
3. Hinge line: Short and curved
4. Dentition: Edentulous
5. Adductor impression: Kidney shaped adductor centrally present,monomyrian
6. Pallial line: Absent
7. Ventral margin: Crenulated

8. External ornamentation: Irregular radial rib and concentric lines are present
9. Special character: Edentulous,centrally present kidney shaped adductor,concentric lines and irregular radial rib are present
10. Name of the genus: OSTREA
11. Bio-status: Phyllum-Mollusca
                            Class-Pelecypoda
12. Range in time: Triassic to present
13. Indian horizon: Ranikot formation of lower Eocene

EXOGYRA:

Fig:Exogyra

1. Shell form: Orbicular
2. Umbo: Slightly pointed to posterior
3. Hinge line: Short curve
4. Dentition: Edentulous
5. Adductor impression: Monomyrian
6. Pallial line: Absent
7. Ventral margin: Smooth
8. External ornamentation: Concentric line present and radial rib present
9. Special character: Orbicular cell form, umbo is slightly pointed to posterior, short curved hinge line, dentition is edentulous, adductor impression is monomyrian and pallial line is absent
10. Name of the genus: EXOGYRA

11. Bio-status: Phyllum-Mollusca
                            Class-Pelecypoda
12. Range in time: Triassic to Eocene
13. Indian horizon: Ariyalur formation of cretaceous of trichinopoly

PLICATULA:

Fig:Plicatula

1. Shell form: Triangular
2. Umbo: Straight
3. Hinge line: Short and curved
4. Dentition: Not distinct
5. Adductor impression: Not distinct
6. Pallial line: Not distinct
7. Ventral margin: Round
8. External ornamentation: Radial rib and concentric lines
9. Special character: Triangular shell form,umbo is straight,short and curved hinge
line,adductor muscle not distinct.Rounded ventrsl margin.

10. Name of the genus:PLICATULA
11. Bio-status: Phyllum-Mollusca
                              Class-Bivalve
12. Range in time: Triassic to recent
13. Indian horizon: Bagh beds to cretaceous