BRACHIOPODA. 171 
The principal distinction presented by this species, and I believe of the whole genus, 
is the internal septum or septa of the smaller valve; and the loop is said to connect or to 
be supported by these thickened internal processes, so that the apophysary system is 
somewhat variable in different species; but the loop is so delicate in these small shells 
that itis very rarely preserved, even in the recent specimens, and they are not present in 
my fossils. ‘The byssal aperture is very large in this species, so also are the hinge- 
denticles. The dorsal margin of the smaller valve is. nearly straight and entire, the inner 
margin of this valve being crenulated all round up to the dorsal edge, and the valve is 
divided into two equal parts by a large and prominent septum. Mr. Jeffreys has lately 
referred the Crag shell with doubt to /unzfera, a Mediterranean shell (‘ Rep. Dredg. among 
the Shetland Islands, 1868’); but there is great doubt about dunifera, so that I have 
retained my original name of czsfe//ula, which, Mr. Davidson tells me, he also intends 
to do. 
RHYNCHONELLA PSITTACEA, Chemnitz. Supplement, Tab. XI, fig. 2 a—c. 
RHYNCHONELLA Pstpracea, Davidson. Brit. Tert. Brach., p. 21, 1852. 
Diam. $ inch. 
Localities. Red Crag, Sutton. Fluvio-marine Crag, Bramerton, Thorpe and Postwick. 
Chillesford bed, Bramerton. Upper Glacial, Bridlington. Post-glacial, March. 
This species is not abundant as a British fossil, and the valves are generally separated, 
although occasionally the two have been found united. It has considerable range as a recent 
species, but it is confined to the colder regions of the northern hemisphere. A species 
much resembling it has, however, been found in the southern hemisphere. 
There is no loop to this shell, the spiral arms being attached to two small curved pro- 
cesses projecting inwards from the umbo of the imperforated valve; the hinge-teeth of the 
beaked or larger valve are very strong, and they are supported, as it were, upon a sort of 
partition extending from the base of the hinge-teeth towards the tumid portion of 
that valve, by which a strength is given to this shell which I have not observed in other 
Brachiopoda ; for what especial purpose, however, this is used I am not able to say. The 
beak of the larger valve appears to have retained its infant condition, and is not worn 
away like that of Zerebratula. My. Bell gives the shell from the Red Crag of Sutton 
(‘Ann. and Mag. Nat. Hist.,” Sept., 1870), and Dr. Woodward, im his list in ‘ White’s 
Directory,’ gives it from Thorpe and Postwick. Mr. Reeve has found it, but rarely, in 
both the beds at Bramerton, and Mr. Harmer found it at March; Dr. Woodward gave 
it (Geol. Mag.,’ vol. i, p. 53) from Bridlington. 
coy) 
23 
