Mr. T. Davidson on Recent Terebratulae. 31 



that the prolongation of the septum, which in T. flexuosa is 

 similar to that in T. crenulata or in T. Valenciennesii, is not only 

 liable to vary in different species of Terebratella, but likewise 

 in specimens of the same species. This subject will assuredly 

 demand further examination ; for if T. flexuosa is only a young 

 or half-developed condition of T. magellanica in which the sep- 

 tum was prolonged, to be so no longer as the shell approached 

 the adult state, then I am of opinion that T. Valenciennesii 

 and its synonym T. Evansii should be considered in the same 

 light with reference to T. cruenta, of which it would be, in that 

 case, the young. The material at my disposal will not, however, 

 enable me to express a decided opinion upon the question ; but 

 as T. cruenta does not appear to be rare in Cook's Straits, New 

 Zealand, it will not be very difficult for some naturalist in that 

 island to procure a series of specimens at all ages, so as to deter- 

 mine the question. Our difficulties do not end here ; for the 

 shell described by myself, with much reserve, as Terebratella"? 

 Cumingii, and which Dr. Gray subsequently located with Magas, 

 and Mr. Reeve with Bouchardia, possesses a loop and septum 

 similar to that of several species of Terebratella, but with the 

 general external shape, prolonged beak, and terminal foramen of 

 Bouchardia, from which last-named subgenus it differs, however, 

 very materially in its interior details. In 1852, while describing 

 this New Zealand species, I felt much puzzled ; for, on the whole, 

 it is evident that this shell is intermediate between Terebratella, 

 Trigonosemus, Bouchardia, Magas, and another of those forms 

 which, according to my possibly erroneous notions, radiate from 

 or cluster round a common type, and which cannot be considered 

 as distinct genera, but merely as subgenera of Terebratella, and 

 to which they are certainly more or less intimately related. 



Indeed, the differences of the interior dispositions in T. ? Cu- 

 mingii and Bouchardia appear to me greater than those which 

 exist between it and Terebratella; and I should consequently 

 still feel disposed provisionally to leave it under the last- 

 named subgenus, although its position there may be somewhat 

 abnormal. 



We are now insensibly led on to inquire, what is the character 

 of the loop of Megerlia ? and here we find it to be three times 

 attached, first by its crura to the hinge-plate, secondly to a me- 

 dian septum by means of horizontal processes, as in Terebra- 

 tella, and from thence reflected to become attached for the 

 third time, by the lateral portions of the loop being again 

 fixed to the septum. In fact, were it not for this third attach- 

 ment, which may not have existed in the fry or young state, 

 we should at once, as far as the loop is concerned, consider Me- 

 gerlia to be a synonym of Terebratella. My friend Mr. Reeve, 



