165 



possessing transparency, at Montmorency, Erappes, &c. Lamarck 

 observes, that it has the form of a very small seed of some species of 

 lucern ; and, hesitating at determining it to be really a multilocular shell, 

 only assumes it as such for the present. At Fig. 24 is represented one 

 of its detached carinated ribs, 



LETTER XIII. 



BIVALVES WITH EQUAL VALVES, AND REGULARLY FORMED 



PINNA MYTILUS MODIOLA ANODONTA UNIO NU- 



CULA PECTUNCULUS A RCA CUCULLCEA TRIGONIA 



TRIDACNA HIPPOPUS C AUDIT A ISOCARDIA CARDIUM 



CRASSATELLA PA PHI A LUTRARIA MACTRA ERYCINA 



I'ETRICOLA DON AX TRIGON ELLITES VENUS....C YTHERE A.... 



VENERICARDIA CYCLAS LUCIN A.....TELLINA CAPS A SO- 

 LE N SANGUINOLARIA GLYCEMERIS MY A. ...PANOPEA. 



W E now proceed to the examination of the fossil remains of bivalve 

 shells, the dwellings of acephalous molluscae, having no distinct head, 

 and therefore unprovided with eyes, ears, &c. 



Bivalves, with equal valves. 



XCII. Pinna. A cuneiform, longitudinal bivalve, with an acute base, 

 gaping in the upper part : the hinge without a tooth, lateral, and very 

 long : the valves coalescent. 



One species only, P. margaritacta, Lam. is found in fragments, at 

 Grignon. Specimens which may be referred, perhaps, to the same 

 species, are found in the cliffs in the neighbourhood of Bognor : these 



