U2 



THE GEOLOGIST. 



The third stage may be observed in fig. 4, where the different 

 parts are still more developed, but the mesial plate has not yet 

 reached the bottom of the valve. 



By gradual changes we are thus conducted to the fourth stage, 

 fig. 5, where the loop has attained its complete development. The 

 central plate, which was freely suspended in the shell before, has 

 now reached and become soldered to the bottom of the valve ; the 

 first pair of lamellse are still attached to its upper sides, and the re- 

 flected portion of the loop has become fully developed, the extremities 

 facing the front of the shell being considerably prolonged, as is seen 

 in fig. 5 of our plate. Numerous long spines also project from the 

 outer edges of the lamellae and loop, giving to the interior a very 

 peculiar appearance. 



The subject of the development of the internal calcified supports in 

 brachiopoda is of considerable interest, and much may yet be learnt 

 by a careful study of recent specimens of this class. The importance 

 of attention to the subject is the greater when it is remembered that 

 the classification of many of the brachiopoda depends more upon in- 

 ternal than external form, and that had the different stages of 

 development shown by the Terebratella Buchiianii been observed 

 under other circumstances, or from beds of different geological ages, 

 each would probably have been constituted a distinct genus. 



The Terebratella Buckmanii is the prevailing shell at Hampton 

 Clift's, and many hundred specimens have passed through my hands. 

 It has before been remarked that the young of Terehrahda maxillata 

 also occur at Hampton, though this species is comparatively rare. 

 It requires considerable experience to determine by the exterior to 

 which genus the different shells belong. Both possess the same 

 contour, and are strone^ly punctuate. In general, however, the 

 Terehratella Buchmanii may be distinguished by a dark longitudinal 

 line in the centre of the ventral valve, due to the mesial septum, 

 and by the characters previously noticed when speaking of Terehra- 

 tula maxillata. 



It is due to my friend Mr. Woodward I should remark, that whilst 

 my investigations on this shell were in progress, having been the 

 means of conveying a series of them to him, he noticed it to be a 

 Terebratella ; and in a communication to Mr. Davidson suggested 

 the specific name of Terehratella Buchnanii for it, which I have much 

 pleasure in adopting. 



Teuebratella furcata. Sow. and Moore. PI. xiii., figs. 8-10. 

 TcreJjratula f areata, Sow. ; T. orhicularis, Sow. ; T. carcliiim, Lamarck. 



Shell small, rounded — both valves moderately convex ; valves 

 conrsoly plicated, varying in number, and may be seen on the inner 

 side, bifurcating occasionally ; surface punctuated ; beak truncated ; 

 Ibramon largo ; loop doubly attached. 



This lil ilo shell was originally figured by Sowerby under the name 



