90 



and it is equally clear that had it, while attached, extended it forwards 

 in the manner which it adopts when free, and to the same degree in the 

 same time, it must have recurved upon itself, until its further growth 

 would have been arrested, and respiration impossible. Granting, 

 therefore, that this be true, it follows that the animal possessed 

 an intuitive perception of the exigencies of its position, and, to a 

 certain extent, the power of accommodating itself to them. 



We see, for instance, in the examples before us, that, unable to pro- 

 vide that normal degree of concavity which is proper to the larger 

 valves, the creatures compensated themselves for the circumscription, 

 by giving an unusual convexity to the smaller valve, a corresponding 

 degree of lateral expansion to the larger, and retaining throughout the 

 period of their existence, those modifications of form which were rightly 

 special only to a portion of it.* 



Here naturally arises the question, whether the young animal could 

 of its own volition free itself from connection with the body to which it 

 had attached itself, and this we think may be answered affirmatively, 

 from the fact, that, in the majority of instances, that connection could 

 have endured but for a short time. The primary point of adhesion 

 must in general have been so small in the young fry, and applied to 

 surfaces so even, that a very slight exertion of force of any kind, either 

 voluntary or involuntary, would have sufficed to detach it ; but we can 

 readily conceive that in the event of adhesion taking place to uneven 

 surfaces, as shown in figures 5 and 6, Plate 2, and fig. 1, Plate 3, 

 where rugosities of the kind suggested exist in every part of the valves 

 of each, the union between the two bodies, must have become so 

 complex as to render separation impossible, except by the application 

 of very considerable force. 



In the event of contact remaining tumaturally prolonged, as in the 

 case of Ostrea Iseviuscula and irregularis of Munster, the foregoing 

 observations would in all cases properly apply. 



Quenstedt's figures of Ostrea iiTegularis and rugata (Der Jura, table 

 3, figure 15, a, b, and f. 18, and those of Chapuis and Dewalque)f are so 

 evidently taken from imperfect individuals of this species, that more than 

 a reference to them is unnecessary, Quenstedt's figure 16 resembling so 

 closely our figure 5, Plate 2, as to appear, upon a cursory view, to 

 have been copied from the same specimen. The shells usually labelled 

 as G. suilla, appear to be selected from the small flat-looking examples 

 before referred to as occui-ring abundantly in certain localities with 



* Compare relative length and breadth of Figure 1 and Figure 4, Plate iv. 

 t Description des Fossiles des Terrains Secondaires de la Proyince de Lnxembourg. 



