MOORK — ON NEW lllUClIIOI'dDA, lO'l'C. 
441 
Mr. Davidson. It will be seen from wliat follows that two species at 
least of Tcrebratella are to bo found in these beds ; but when D'Or- 
bigny placed the Terehratuhi hemisj)]icerica in this genus, he could 
not have seen its interior, which, in several examples I possess, have 
the short and simple loop of Terebratula, and tlie sbcU in question 
Avill therefore have to return to its oi'iginal position. 
Terebratella, 
Terebratella Buckmanii. "Woodward, MS. PI. xiii., figs. 1-5. 
Shell generally a little longer than wide, rounded in front, and 
tapering to the beak ; valves moderately convex ; beak short, very 
slightly inciTrved and truncated by a foramen, suiTOunded in part by 
the extremity of the beak, the umbo of the dorsal valve, and two 
small labral deltideal plates. Internally the adult shell is provided 
with a doubly attached loop, the first pair of lamellce extending con- 
siderably before becoming reflected to form the loop. Shell struc- 
ture punctuate. Dimensions of the largest "example hitherto 
observed : length, 3| lines ; width, 3 lines ; depth, 1| lines. 
Ohs. — I had collected a considerable number of these little 
brachiopods from the oolite of Hampton Cliffs, under the idea that 
they were the young of the Terehratula maxillata, my object being 
to prepare dissections showing the loop of that species. I was much 
interested in finding in the example I first opened that it could not 
belong to the young of that genus, although outwardly it is almost 
undistinguishable from it. The difference in the loop proved it to 
be a true Terebratella. My observation does not show that it 
attained larger dimensions than those mentioned, but it had then 
assumed the character and development peculiar to the loop which 
characterizes the genus to which it is referred. In an early stage of 
my examination, modifications in the shape of the loop were noticed, 
and observations extending to several hundred specimens resulted in 
shovsdng the curious changes effected by age in the form of the loop, 
which may be seen by referring to plate xiii., figs. 2, 3, 4, and 5. 
The first stage of development I have been able to observe is 
sketched in fig. 2. Therein it may be perceived the two first lamella) 
are united to the hinge-plate, and to a free rudimentary mesial plate, 
which is, in fact, the first origin of what at a later period becomes a 
mesial plate. In this state it is free, and does not touch the bottom 
of the valve, although when viewed in profile spines may be seen 
passing downwards, which afterwards join the mesial septum. 
The loop has not yet been formed, but a plate projects between 
the lamella), and appears as if longitudinally split to a certain depth 
in the centre. 
The second stage is exhibited in fig. 3. In this we find the two 
lamellse with the rudimentary plate as in fig. 2, and, besides, the 
origin of the reflected portion of the loop, presenting in this first 
stage of its development but a very small and rudimentary aspect. 
VOL. III. 3 K 
