152 
TUE GEOLOGIST. 
complex as to render separation impossible, except by the application of 
very considerable force. 
In tlie event of contact remaining unnaturally prolonged, as in the case 
of Ostrea l^Binuscula and O. irremilaris of Miinster, the foregoing obser- 
vations would in all cases properly apply. 
" There can be no doubt, that the great confusion of ideas which has 
existed with regard to what we consider to be one species, as evidenced 
by the hosts of synonyms for it, to which we have been compelled to re- 
fer, arose from that love of species-making which characterized most of our 
earlier palaeontologists. JSTo sooner did an abnormal form present itself, 
than it was seized upon and named as a new species, whilst the examina- 
tion of the series would have shown its true connection with common types. 
In species of which the number varies so much individually, as in the 
oyster-tribe generally, this precaution is most essential, to enable us to 
arrive at safe conclusions in this respect : the most symmetrical forms 
having been set up as types, whilst, in point of fact, these are rather ex- 
ceptional than otlierwise. 
*' "We can convince ourselves," Mr. Jones concludes, "in the instance of 
G. incurva, that this shell is capable of assuming every shape between that of 
a flat oyster and one of so different a development as to have suggested 
the propriety of conferring upon the individuals exhibiting it, a distinct 
genenc name. It has been shown, how the entire character of the shell 
has been effected, by circumstances which enforced upon it a more or less 
permanent adhesion to the body to which it had primarily attached itself ; 
that the lateral fuiTow, upon the presence or absence of which specific 
differences have been supposed to depend, is one of the most fallacious 
characters upon which they can be based. We can perceive that tlie dif- 
ferences between the assumed species G. incurva, ohliquata, Maccul- 
lochii, and cymhium, are less than those existing between the young, half- 
grown, or adult states of either. We know that other creatures, inhabit- 
ing the same sea-zones, pass upwards from the point at which they first 
appear, through a greater, or at least as great, a strati graphical range as 
either of these. Do we not then rightly pause before we draw sharp lines 
of demarcation, whilst neither the facts presented to us in tlie formation 
under consideration, nor our knowledge of physiological facts, as exempli- 
fied in the existing life of our own epoch, afford us any valid pretext for 
80 doing ?" 
To show in the clearest possible manner the nature of these differences, 
Mr. Jones has constructed a diagram, representing Gryphapa incurva of 
the best known-type and fullest dimensions. By uncovering the drawing 
from its younger portion upwards, may be made to appear in succession, 
fibrst, its oyster condition ; secondly, that of Gryphaa suilla ; thirdly, that 
of G. ohliqua, young ; fourthly, that of G. ohliqua, adult ; fifthly, G. 
incurva, half-grown ; sixthly, ditto two-thirds grown ; seventhly, adult ; 
eighthly, in its most aged form. A comparison of any of the forms we 
have referred to, made by placing almost any two shells of different sizes 
in juxtaposition, so that the curves of their beaks shall be as nearly as 
possible parallel, will exhibit the same difference of degree between them, 
in quite as satisfactory a manner. 
The names by which the numerous varieties have been hitherto known, 
and under which they are figured, Mr. Jones suggests, may admit of use, 
as those of varieties only of G. incurva, as which they ought to be gene- 
rally recognized. The results of Mr. Jones's investigations then may be 
thus stated, that not only is there no clear distinction between these so- 
called species when studied in a fairly selected series ; that no particular 
