474 Mr. T. Davidson on the yenus Waltonia. 



XLII. — On the genus Waltonia. By Thomas Davidson, Esq. 



[With a Plate.] 



M. Bouchard and myself, in Jan. 1848*, published a detailed 

 description of the genus Magas, Sowerby, with figures illustra- 

 ting the internal structure of this remarkable little shell, at that 

 period incompletely known. Some time after I wrote a paper f 

 with figures on a recent species known under the name of Tere- 

 bratula rosea, which shell, from the peculiar arrangement of its 

 internal organization differing from that of all known Brachio- 

 poda, led me to propose for it a distinct generic name, that of 

 Bouchardia, belonging to the family of Magasida ; Magas pu- 

 milus and Bouchardia rosea being the only species in each genus. 

 During a late visit to Paris, M. Valenciennes kindly lent me 

 specimens of recent Terebratula brought to Europe by Quoy and 

 Gaimard ; and on a tablet on which were placed several specimens 

 of Terebratula sanguinea, Leach, I found a small shell whose or- 

 ganization was completely different from those with which it was 

 surrounded, but offering characters not allowing of its being 

 placed in either Magas or Bouchardia, but claiming a new 

 generic name, and forming part of the family of Magasida. 

 M. D'Orbigny, in his 'Pal. Franc. Ter. Cretaces/ vol. v. p. 52, 

 places in this family Magas and Terebratulina ; I cannot however 

 agree with that author in this association, as I consider the orga- 

 nization of Ter. Caput serpentis to be completely different from 

 that of Magas, and not to belong to the same group or family. 

 In a very interesting paper by Mr. King % on certain genera of 

 Palliobranchiata, the internal organization of Terebratula rosea 

 is alluded to ; and in the great work by that author on the 

 Permian fossils of England, Mr. King has adopted and placed 

 in the same family of Magasidce the genus Magas, Sow., and my 

 Bouchardia. 



Genus Waltonia. 



Char. Shell bivalve, inequivalved, equilateral, subovate, slightly 

 convex ; beak almost straight, partly truncated by a large foramen 

 extending from the summit to the umbo of the ventral valve 

 which it partly encircles ; deltidium small, disunited, and forming 

 only a portion of the peduncular opening : at the base of the beak 

 are two strong teeth corresponding with the sockets of the ventral 

 valve. The interior of the dorsal valve is simple, with a slight 

 central longitudinal elevation dividing the shell into two equal 

 portions, not extending quite to the margin. In the ventral valve 



* Bull. Soc. Geol. de France, vol. v. 2nd series, p. 139, pi. 2. 



t Ibid. vol. vi. 2nd series, 1849. 



% Annals and Mag. of Nat. Hist. vol. xviii. IS 1(5. 



