30 Mr. T. Davidson on Recent Terebratulse. 



septum, by processes given off at right angles near the centre of 

 the valve, the remaining portion soon becoming reflected, as in 

 the type, Terebratella magellanica. Now, in this species, as in 

 very many others, the dispositions of the loop are exactly the 

 same, the septum being but slightly raised above the surface of 

 the valve where the second attachment takes place, and not ex- 

 tending above or beyond it. Such is Terebratella proper, which 

 will include, besides many fossil forms, the recent T. transversa, 

 T. omenta, T. Bouchardii, T. rubella, T. i-ubicunda, T. coreanica, 

 T. labradorensis, T. spitzbergensis, T. frontalis, and T. caurina. 

 But was not the arrangement above described liable to certain 

 modifications ? I should say it was ; for in some shells, such as T. 

 Valenciennesii=^ T. Evansii, T. crenulaia, T.flexuosa, the septum, 

 after the second attachment of the loop, rises and extends more 

 or less rapidly in the form of a narrow elevated plate, and in 

 some examples reaches the centre of the perforated or ventral 

 valve, as in Magas, while the loop and other dispositions are 

 exactly similar to those of Terebratella proper. This extension 

 of the septum cannot, in my opinion, be regarded as of any 

 generic or even subgeneric importance; and I therefore con- 

 sidered Dr. J. E. Gray was not justified (in his ' Catalogue of the 

 Terebratulse of the British Museum^) in removing the above- 

 named species from Terebratella and placing them in Magas — 

 an arrangement which Mr. S. P. Woodward did not adopt in his 

 excellent Manual. In his first paper and monograph, Mr. Reeve 

 had followed Dr. Gray, from not having " sufficiently understood 

 the fossil type of Magas;" and w^hile restoring T. Valenciennesii 

 or Evansii and T. crenulata to Terebratella (to which they evi- 

 dently belong), he has added that, while the loop is a little re- 

 moved from the typical loop of Terebratella, as seen in T. magel- 

 lanica, it is at least intermediate in its characters between 

 that and Magas. This, however, would relate solely to the ex- 

 tension of the septum; for in Magas (not hitherto known in the 

 recent condition, but of which there are several fossil species), 

 what corresponds to the reflected portion of the loop is anchor- 

 shaped and disunited*. Magas may be, and probably is, a 

 modification of Terebratella, but sufficiently constant and distinct 

 to be retained as a subgenus. 



Before we leave the subject in connexion with the extension 

 of the septum, as exemplified in T. crenulata, it must be observed 

 that several authors, among whom we may quote Prof. Suess 

 and Mr. Beeve, have considered T.flexuosa to be a synonym of 

 T. magellanica ; and if such is the case (and I am not prepared 

 to deny the probable correctness of the view), they are admitting 



* As described and illustrated by M. Bouchard and myself in the ' Bid- 

 letin Soc. Geol. de France,' vol. v. 2nd series, 1848. 



