OSTREA. 



Neither the general shape of the valves nor the particular form of the muscular scars 

 (which follows or is modified by the varying outline of the shell) are available as distinguishing 

 characters in this very difficult genus ; colouring appears to be of more than ordinary value for 

 essential distinction. The number of recorded species is not large, and a considerable 

 proportion of those constituted are founded on the accidents of age and growth. An 

 examination, at Paris, of the originals of the meagre descriptions in the ' Animaux sans 

 Vertebres' will corroborate my assertion. 



PLATE I. 



1. 4. Ostrea rhizophorse of Guilding (Zool. Journ.). 



2. Ostrea bicolor of Hanley (Proc. Zool. Soc. 1845). 



3. Ostrea multistriata of Hanley (Proc. Zool. Soc. 1845). 



PLATE II. 



5. Ostrea frons of Linnaeus (Syst. Nat.). 



6, 7. Ostrea iridescens of Gray (on tablet in British Museum) ; margaritacea ? of Lamarck. 

 8. Ostrea edulis, var. purpurea ? 



It is not improbable that this beautiful oyster may eventually be distinguished as a 

 new species : I cannot find any published account of it. It has the general aspect of 

 edulis, but differs in its colouring, which, upon the lower valve, where the lamellae are 

 quite loose, and beautifully festooned in large gathers, is of a rich uniform purple ; upon 

 the upper one, where the lamellae are loosely appressed, is of a purplish liver-colour, that 

 becomes intensely purple at the beak, where the lamellae are abraded. The interior is of 

 an uniform dirty white, with a simple margin, and only rudimentary denticles at the apex. 

 The example, which is rather light, was purchased as from Toulon, and was attached to 

 a stick, which accounts for the uninterrupted expansion of the lamellar foliations. It 

 closely resembles also some specimens received from Philippi as the cristata of his 

 ' Enumeratio,' which I unhesitatingly refer to the common rock oyster of our own coast. 



PLATE III. 



9, 12. Ostrea Sinensis of Gmelin (Syst. Nat.). 

 10, 11. Ostrea (Gryphaea) angulata of Lamarck (Anim. s. Vert.). 



