CLASSIFICATION OF THE BRACHIOPODA. UI 



depression, in the anterior lialf of the thickened valve are excavated tvro conical hollows, 

 which correspond to the cones of the attached valve, and like them are separated by 

 a rounded mesial ridge, united near the front to the raised border which surrounds the 

 valve. 



Obs. M. de Verneuil was the first to draw attention to the shell above described, by 

 publishing a figure of the lower valve of a specimen from the Eifel,^ which he classed 

 with doubt in Leptana, adding, " that the spiral arms loere coiled Jive or six times 

 on each other, and placed in the attached valve, so as to rise perpendicularly against the 

 smaller one ;" the author having kindly presented me with one of his four examples, M. 

 Bouchard founded on it the genus Davidsonia,^ for which compliment I feel greatly 

 obhged to my old and distinguished friend. M. Bouchard clearly proved that the shell 

 was not a Leptana, but it must likewise be observed, that at the period above-mentioned 

 only the lower valve was known, so that the description was naturally incomplete ; but 

 this blank was some time after filled up by M. de Koninck's fortunate discovery of two 

 upper valves.^ 



Much difference of opinion has been expressed as to the nature of the various impres- 

 sions visible in the interior of the shell, as well as to the systematic position of the genus. 

 M. de Verneuil's original view of the massive cones has already been noticed. M. 

 Bouchard believes that they were produced by secretions deposited by the posterior adductor 

 muscle, while M. de Koninck sees in them nothing more than the common thickening of 

 certain portions of the valves in other Brachiopoda, such as Bouchardia rosea, &c. ; 

 and Professor King states, that he is "still in favour of these cones having been produced 

 by labial processes!'^ 



Some authors believe that the arms could not have influenced the 

 form of the shell ; but the absence of such impressions in recent forms, is 

 no argument against the possibiUty of such occurring in some of those 

 extinct species, where, as in Davidsonia, so small a space remains for 

 the animal -^ nor do I think it possible that the labial appendages could 

 have occupied any other space than the small one existing between 



,1 1 ii J. J.1 ill • , I p - 1 Section of Davidsonia, 



the cones ; and that the mantle, by pressmg on the free spu^al arms, in the eoUecdon of 



retained some impressions of their coils, which were transmitted to the tpfcl'^ieftwhiJbl 



shell it was secreting : and this view appears the more probable, since aT"onu,^ oneTem- 



the vascular trunks and veins existing on the mantle, were likewise im- pied by the animal ; 



o ' ^ "-"^ '" f. IS the portion at- 



pressed on the outer sides of the cones as well as on other portions <acAerf. 



' Geol. of Russia and the Ural Mountains, vol. ii, p. 227, pi. xv, fig. 9, 1845. 



- Memoir sur un Nouveau genre de Brachiopode, &c., ' Anuales des Sciences Nat.,' vol. xii, p. 84, 1849. 



^ Notice sur le genre Davidsonia, 'An. de la Soc. Royale des Sciences de Liege,' vol. viii, p. 149, 

 1852. These valves are now in the British Museum. * Monograph of the Permian Fossils, p. 151, 1849. 



'•> Similar impressions occur in certain examples of Productus and Strophomena, and which may be 

 attributed to the same cause. 



