174 DESCRIPTION OF SHELLS. 
Colour is of so rare occurrence among Oysters, and especially among fossils, 
that we are glad to accept it for a specific mark: the present shell belongs to 
a section of the genus which contains species whose surfaces are not imbricated, 
but covered by a continuous plate of a fibrous structure ; in this the structure 
is however obscure, in O. tabulata and O. dorsata, &c., it is very easily detected. 
Old shells seem to be imbricated, because the edges of the laminz are worn away. 
The surface of the young shell, well shown in an individual which has been 
attached to a large Nautilus, is nearly smooth, but irregularly marked with 
distant, short, interrupted striz ; the hinge-area projects into the cavity of the 
shell. 
Length 3 or 4 inches. 
Ostrea longirostris. (Tab. IV. fig. 4.) 
This is a remarkable specimen from the Cabinet of Mr. Hill the Curator of 
the Chichester Museum ; a portion having been split from the inner surface, has 
disclosed two pearls imbedded in the portion to which the adductor muscle was 
attached. In the figure this slice has been turned over to show their position. 
Ostrea radiosa, Desh. 
Resembles Ostrea pulchra of ‘ Mineral Conchology,’ t. 279, but is a longer- 
shaped shell, and has a larger hinge-area and longer muscular impression ; the 
radiating undulations are also more numerous, more defined and more angular. 
Ostrea elegans, Desh. 
Is intermediate in several respects between the O. radiosa and O. Flabellula, 
but has more plaits than the latter. I much doubt the propriety of separating it 
as a species. 
Ostrea dorsata, Desh. 
This and the following belong to the same section of Ostrea as O. picta, di- 
stinguished by a thick, generally striated coat, which is so fibrous as to resemble 
the shell of Pinna: there are one or two recent species of the same section ; 
they are of a dull purple colour, and very little imbricated. 
Ostrea tenera. (Tab. IV. figs. 2 & 3.) 
The Woolwich type of this species is generally smooth, like fig.3; but I have 
