Mr. J. Morris's Palaonto luteal Notes. 85 



has some resemblance to several of the shorten Arcomyas, and 

 more especially to the figure of A. ensis, Etud. Crit. t. 9. fig. 4-6 

 (misprinted A. brevis), but the valves in that shell are less com- 

 pressed and the umbones are more gibbose : our species how^.sr 

 cannot be an Ar corny a, for M. Agassiz has satisfied himself, from 

 an examination of numerous moulds, that the hinge of that ge- 

 nus is without teeth ; we have fortunately succeeded in clearing 

 the hinge of the shell itself in more than one specimen of Arco- 

 mya, and are enabled to add our humble testimony to the same 

 effect. There remains to be noticed a shell whose resemblance 

 to our species is so considerable, that little doubt can exist that 

 both belong to the same genus ; this is the Psammobia laevigata of 

 Phillips, figured at pi. 4. fig. 1. vol. i, of the ' Geology of York- 

 shire/ The resemblance of the external form to Psammobia must 

 be allowed, and the hinge characters, though distinct from the 

 Psammobia, are more nearly allied to its subgenus Psammotea, 

 which has no tooth in the right valve ; but the figure of the tooth 

 and pit in the recent shells will be found to be very different to 

 our fossil ; the Psammobia likewise have an elevated nymphal cal- 

 losity supporting the ligament which is wanting in the fossil. 



Though rare, our species was gregarious; several specimens 

 occurred in near proximity. Height 13 lines, lateral diameter 

 17 lines. 



Locality. Rodborough Hill near Stroud, where it occurs in 

 the upper ragstone of the Inferior Oolite. 



IX. — Palceontological Notes. By John Morris, F.G.S. 



[With a Plate.] 



The following notes relate to some new or little-known orga- 

 nisms of the chalk, and are chiefly contained in the collection of 

 Mr. Wetherell of Highgate : — 



Thecidea, Defrance. Thecidium, Sow. 



The genus Thecidea, established by Defrance for certain Tere- 

 bratuliform shells with a peculiar apophysary system, is very rare 

 in a recent state, one species only having been obtained from the 

 Mediterranean. The fossil species are not numerous : Bronn 

 enumerates eight species, one from the Jurassic and seven from 

 the Cretaceous formations. In this country the genus has only 

 been recently noticed : Mr. Moore of Ilminster has discovered 

 four in the Lias, and two others have been found in the Inferior 

 Oolite, all of which are described and figured by Mr. Davidson * ; 

 to these, another is now added from the Chalk. 



* Palajontographical Society, Article Brachiopoda. 



