442 
THU 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 arc thus conducted to the fourtli 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 lamella) 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. Niimerous long spines also project from the 
outer edges of the lamella) and loop, giving to the interior a very 
peculiar appearance. 
The subject of the development of the inteimal 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 foian, and that had the different stages of 
development shown by the Terehratella Bucliinanll been observed 
under other circumstances, or from beds of different geological ages, 
each would probably have been constituted a distinct genus. 
The Terehratella Biickmanii is the prevailing shell at Hampton 
Cliffs, and many hundred specimens have passed through my hands. 
It has before been remarked that the young of Tcrehratula tnax 'dlata 
also occm' 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 strongly punctuate. In general, however, the 
Terehratella Buchnanii 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 Terebra- 
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 
Terehratella ; and in a communication to Mr. Davidson suggested 
the specific name of Terehratella Buckmanii for it, which I have much 
pleasure in adopting. 
Terebratella furcata. Sow. and Moore. PI. xiii., figs. 8-10. 
Terohratula furcata, Sow. ; T. orhicularis, Sow. ; T. cardimn, Lamarck. 
Shell small, rounded — both valves moderately convex ; valves 
coarsely plicated, varying in number, and may be seen on the inner 
side, bifurcating occasionally ; surface punctuated ; beak truncated ; 
foramen large ; loop doubly attached. 
This little shell was on'ginally figured by Sowcrby under the name 
