152 



THE GEOLOGIST. 



complex as to render separation impossible, except by the application of 

 very considerable force. 



In the event of contact remaining unnaturally prolonged, as in the case 

 of Ostrea IceviuscuXa and O. irregularis 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. JN"o 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 otherwise. 



" 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 

 generic 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 furrow, 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 the dif- 

 ferences between the assumed species G. incurva, obliquata, Maccul- 

 lochii, and cymbium, 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 the 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 

 so doing p" 



To show in the clearest possible manner the nature of these differences, 

 Mr. Jones has constructed a diagram, representing Grypliaa 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, 

 first, its oyster condition; secondly, that of Gryph&a suilla ; thirdly, that 

 of G. obliqua, young; fourthly, that of G. obliqua, 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. J ones 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 



