540 PROCEEDINGS or THE GEOLOGICAL SOCIETY. 



only one moderately perfect, showing the exterior, which is from the 

 Brocastle Liassic conglomerate. It occurs also (but fragmentary) in 

 the Charterhouse Liassic mine, and in the Lower Lias at Stout's 

 Hill. 



7. DisciNA Davidsoni, spec. nov. PI. XYI. fig. 29. 



Shell small, rather elongate, ovate, conical ; vertex much elevated, 

 almost central ; anterior margin and sides rounded ; posterior margin 

 rather truncated ; surface of the shell covered by very fine concentric 

 lines. 



In general form this shell is not unlike D. Sandersii, Moore, from 

 the Upper-Lias Leptcena- and fish-beds ; but the encircling stride are 

 much finer. This species is widespread, and evidently not uncom- 

 mon. It is usually found attached to the interiors of dead shells. 

 In this way I have it in the body-whorl of a large Cerithium nodu- 

 losum, Moore, from the Ammonites- Bucldandi beds of Shepton Mallet, 

 and also attached to the internal chambers of several Nautili, their 

 casts having been retained on the inner stony matrix. It occurs also 

 in the metamorphosed bed on shells at "Windsor Hill. Another in- 

 stance is in the phragmacone of a very large Belemnite at Southern- 

 down, where its concave side occupies the centre of the chamber, 

 giving it at first sight the appearance of the siphuncle of an Ortlio- 

 ceras. The only free specimen, though not perfect, is from the 

 Lower Lias of Bedminster Down. 



It is named after my friend T. Davidson, Esq., F.E.S., whose 

 noble work on the Brachiopoda does him. so much honour. 



8. Zellania obesa, spec. nov. PI. XYI. fig. 28. 



Shell minute, longitudinally ovate, much inflated ; margin rounded ; 

 deltidium triangular, widely gaping, and encroaching, as is usual with 

 this genus, on both valves ; surface smooth. 



Only one example of this shell has been found. Its very oval and 

 inflated character distinguishes it from the other three Liassic species 

 I have described. But for its very wide deltidium it might have 

 been mistaken for a species of Entomostraca. 



Locality. The Lower Lias of Stout's Hill. 



9. Avicula ntjda, spec. nov. PI. XYII. fig. 19. 



Shell quadrate, oblique ; umbones much raised, anterior, and 

 curving over the hinge-line ; anterior side most convex ; posterior 

 side angulated from the umbo tov/ards a rounded posterior and ven- 

 tral margin ; surface smooth, with faint, irregular, concentric lines 

 of growth ; hinge-hne shorter than the shell. 



Erom a Liassic conglomerate resting immediately upon Carbonife- 

 rous limestone on the Marston road at Holwell, which appears to 

 represent an horizon at the junction of the Lower with the Middle 

 Lias, and of the age of the Hierlatz beds. I have some difliculty 

 in separating this shell from the Avicida quadrata of Dr. von Dittmar, 

 from the Alpine Upper Trias of Hallstadt. 



