App. a.] Dr. FiTTON on the Strata below the Chalk. 341 



wide as it is long, is moderately gibbose, and has a characteristic depression along its middle. 

 The sides gape slightly. 



Fig. 7. Amphidesmal tenuistriatum, A transversely elongated, oblong, very flat shell, with 

 numerous impressed striae, the posterior extremity slightly truncated ; the beaks nearly central, 

 not produced. The genus is rather doubtful. 



Fig. 8. Corbula truncata. Very similar to one, or two, species in the London clay. Its form 

 is oblong- ovate; the posterior side is produced, obliquely truncated, and pointed towards the 

 front. The surface is transversely striated. 



Fig. 9. Mactral angulata. Smooth, subtriangular; the posterior side defined by a ridge; 

 beaks small, nearly close ; hinge unknown. 



Fis. 10. Petricola nuciformis. Suborbicular ; striated longitudinally ; the edge serrated ; the 

 beaks small, sunk into the shell. 



Fig. 11. Petricola canaliculata. Orbicular, very convex, longitudinally furrowed ; furrows 

 nearly covered over edge grasiulated. The concealed furrows are represented in the magnified 

 section; the edges of the costse between them are sometimes connected across the furrows. 



Fig. 12. Psammohial gracilis. Much elongated transversely, nearly cylindrical; surface 

 marked with many raised lines, which are most elevated at their extremities ; posterior side de- 

 fined, produced, and pointed. 



Fig. 13. Lucinal orbicularis. Orbicular; convex; longitudinally striated; striae numerous, 

 often forked ; beaks small, distant ; edge entire. 



Fig. 14. Lucina Pisum. Nearly globose ; fifteen, or more, reflected ridges cross the surface. 



Fig. 15. Astarte concinna. Oblong, convex, concentrically furrowed, thick; lunette elon- 

 gated, deeply sunk ; beaks oblique. In everything, except the elongated form, this resembles 

 Astarte striata, (Min. Conch, t. 520. f. 1.), which is orbicular. 



Fig. 16. Astarte formosa. Orbicular, approaching to triangular, rather flat, with thick edges; 

 about ten prominent reflected ridges on the surface ; lunette elongated, concave. Found in great 

 numbers at Blackdown. 



Fig. 17. Astarte multistriata. Very convex; rather wedge-shaped; with many concentric 

 ridges, and numerous fine longitudinal striae between them ; lunette large and broad. A small, 

 rare species. 



Fig. 18. Astarte impolita. Obovate, convex, rather angular at the beaks : surface anti- 

 quated ; ligament imbedded in a lanceolate groove. 



Fig. 19. Cyprina cuneata. Cordato-cuneiform ; surface even ; posterior side straight, a little 

 produced at its extremity ; beaks prominent ; valves deep ; shell rather thin. The specimens 

 found at Blackdown are seldom larger than the small figure : the large one was in the collection 

 of the late Mr. Goodhall. 



PLATE XVII. 



Fig. 1. Cyprina rostrata. Distinguished by its general form from Cyprina {Venus) angulata 

 (Min. Conch, t. 65.), which it nearly resembles. It is less convex, the posterior extremity is more 

 produced, and the line thence to the beak straighter. 



Fig. 2. Cythercea subrotunda. Flat, lenticular, nearly orbicular, smooth ; lunette elongated ; 

 fulcrum arched. One specimen has an Exogyra adhering to an eroded part of the surface. 



Fig. 3. Venus'! truncata. Rather less convex than V. lineolata (Min. Conch, t. 20.); strongly 

 marked with lines of growth ; the posterior side expanded and truncated ; lunette obscure, 

 lanceolate. 



