Evans — On Cavities in Old River Gravel, 443 



of muscular impressions are visible, excepting those on both sides of 

 the elongated median ridge, and probably the narrow impressions 

 going from the exterior margin of the adductors towards the margins 

 of the valves. It is also possible that muscles were attached in the 

 apical corners of the ventral valve. 



If, however, Trimerella, by reason of the structure of its median 

 muscular impressions, is related to the Lingulidce, it is widely 

 separated from them in another respect, as its dorsal valve is pro- 

 vided with a large tongue-shaped process (possibly the processus 

 cardinalis ?), by means of which it is articulated to the ventral valve. 

 This process fits into a semilunar groove below the area of the 

 ventral valve, and this area is formed by the lamellae, that one by 

 one have been secreted above the semilunar groove (PI. XX. Fig. 7). 



Another anomaly of which I have not seen any homology amongst 

 the Brachiopoda, is that the lateral margins of both valves are grooved 

 by a furrow, shallow at the ends and deepest in the centre. These 

 furrows encircle the opposite margins, and make the valves close 

 more tightly. 



The valves attain a thickness of 15 millimetres, and consist in their 

 perfect state of calcareous spar, and show no traces of any organic 



EXPLANATION OF PLATE XX. 



Interior of ventral valve restored. 



Casts of both valves. 



Cast of dorsal valve of Obolus ? Davidsoni, Salter (Gotland). 



Section of ventral valve at the openings of the siphons. 



Section of the same showing the concentric calcareous secretions around 



the siphons. 

 Cardinal process of dorsal valve fixed in the ventral valve. 

 Side view of dorsal valve. 

 Section of ventral valve at the apex. 

 Interior of the dorsal valve of Obolus, sp. from a cast in gutta-percha. 



Fig 



. 1. 



„2,3. 



» 



4. 



J) 



5. 



» 



6. 



„ 



7. 



J5 



8. 



,, 



9. 





10. 



n. — On some Cavities in the Gravel of the Valley of the 

 Little Ouse, in Norfolk.^ 



By John Evans, F.R.S., F.S.A., Sec. Geol. Soc. 



A FEW months ago both geologists and archgeologists, and espe- 

 cially the latter, were surprised to hear of the discovery in the 

 valley of the Little Ouse, between Thetford and Brandon, of certain 

 cavities in beds of gravel, in which flint implements of the forms 

 peculiar to the Palgeolithic or river gravel were found, and which 

 it seemed possible might have been the habitations of the early race 

 of men who formed these implements. 



An account of this discovery was communicated to the Norwich 

 Geological Society, and also to the Norfolk and Norwich Archaeo- 

 logical Society, by Mr. Sheriff Fitch, F.S.A., F.G.S., to whom the 

 credit of first observing these cavities is due, and who I was in 

 hopes would have made a communication on the subject instead of 

 leaving it for me to do. 



^ Bead before Section C. of the British Association, Norwich, August 23rd, 1868. 



