﻿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 it is 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 lunifera, a Mediterranean shell (' Rep. Dredg. among 

 the Shetland Islands, 1868') ; but there is great doubt about lunifera, so that I have 

 retained my original name of cistellula, which, Mr. Davidson tells me, he also intends 

 to do. 



Rhynohonella psittacea, Chemnitz. Supplement, Tab. XI, fig. 2 a — c. 



Rhynchonella psittacea, Davidson. Brit. Tert. Brach., p. 21, 1852. 

 Diam. f inch. 



Localities. Red Crag, Sutton. Fluvio-marine Crag, Bramerton, Thorpe and Postw 7 ick. 

 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 Terebratula. Mr. Bell gives the shell from the Red Crag of Sutton 

 ('Ann. and Mag. Nat. Hist.,' Sept., 1870), and Dr. Woodward, in 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. 



23 



