VON BUCH ON BEAR ISLAND, 59 



tendon ever higher up and farther from the hinge-border, is not dif- 

 ferent from the lamellae which close the opening of the Spirifer and 

 Orthis, and hence names these, in a way that leads to confusion, the 

 deltidium of the Spirifers. He even goes the length of believing that 

 the perforation of the Terebratulse is to be found also on the Spirifers, 

 under the beak, only on these it is usually grown up. Assuredly 

 this is not the case. When such openings appear on species of Spi- 

 rifer or Orthis, their position is sometimes higher, sometimes lower, 

 often on the side, then again on the point itself ; there is thus no 

 precise law for their situation, clearly proving that they owe their 

 origin only to accidental circumstances. They are also wanting on the 

 greater number of specimens, with no trace of having been grown up. 

 M. de Verneuil tries to prove, that even in the Terebratula the delti- 

 dium is not always convex towards the hinge-border, concave towards 

 the point, from a single species of Terebratula, the T. pectiniformis 

 of the chalk. But in these Terebratulse the two teeth of the ventral 

 valve, as in the Calceola, are united into one elevated double tooth. 

 The deltidium must rise over this tooth ; and this produced an ele- 

 vated medial ridge, by which the strise of growth on the deltidium 

 itself are elevated, and hence appear convex upwards. It is only an 

 appearance ; for each side of the strise of growth is evidently concave 

 upwards. And even were it otherwise, still the mode of growing in 

 Terebratulae from helow upwards, in Spirifer and Orthis from above 

 downwards, would not admit of any parallel between the two modes 

 of growth. Even the long ridge, observable in the middle of the 

 area of Calceola, is named by M. de Verneuil, and by many Ger- 

 man palaeontologists too, a deltidium, and they believe in reality that 

 it is an opening in the middle of the hinge-border, again grown up at 

 a subsequent period. How easily may one convince himself of the 

 contrary ! The strise of growth on the area of Calceola proceed with- 

 out interruption over the medial ridge, but here, in consequence of 

 the slight elevation, are somewhat drawn upwards towards the point. 

 Here also it is again the double tooth of the ventral valve which ele- 

 vates the middle of the area into a ridge. Generally the ridge is in- 

 terrupted ; then the striae of growth proceed forwards horizontally in 

 the interval, which is not possible either in Terebratulse or in Spi- 

 rifer and Orthis. The middle ridge of Calceola has hence never been 

 open, and has nothing in common with a deltidium. 



All these may appear minutiae of no moment ; but they are not so, 

 when we reflect that all the phaenomena of organic forms stand in a 

 necessary causal connexion, and that it is the duty of the naturalist 

 to search out how one character draws all the others along with it as 

 necessary consequences. The knowledge of the true nature of the 

 deltidium of the Terebratulae, with its absence in Spirifer and Orthis, 

 enables us to comprehend the diverse development of all the other 

 organs of these forms, and along with this, why the one lives in the 

 greatest depths of the ocean, the other near the surface of the sea. 

 And in this manner the inconsiderable small deltidium tells us whether 

 in a certain formation we find ourselves on the sea-shore or in the 

 depths of an almost unfathomable ocean. 



[J. N.] 



