NOTES ON THE BRITISH JURASSIC BRACHIOPODA. 251 



MEGATHYRIS, D'Orbignj, 1847. 



Etyra. — /x€ya9, great ; OvpL<;, a small opening. 

 Syn. — Argiopey Deslongcharaps, 1842, non Savigny et 

 Audouin, 1827 ; Argiope (?), Davidson, 1884. 



A pretty little shell found by Moore in the Grreat Oolite 

 of Hampton Cliff ; was provisionally named by Davidson as 

 Argiope (?) oolitica. 



As there is some doubt of its being a Megathyris, we need 

 not concern ourselves about a generic diagnosis of the genus. 

 Davidson's description of this extremely rare shell is as 

 follows : — 



" Shell minute, wider than long ; dorsal valve semi- 

 circular, of moderate convexity. Surface ornamented with 

 thirteen rounded ribs, of which the central one is somewhat 

 the largest. Ribs divided by interspaces of almost equal 

 width ; hinge-line as wide as the greatest breadth of the 

 shell. Ventral valve slightly deeper than the opposite one ; 

 beak nearly straight ; area triangular, flat, moderately 

 broad, with a largish foramen in the middle ; external 

 surface ornamented, as in the opposite one, both valves 

 being crossed by equidistant concentric lines of growth. 

 Length one line ; breadth one and a quarter. Nothing is 

 known of the interior of this small shell" (9, p. 111). 



M. megatrema. Sow. sp., from the Cretaceous rocks, and 

 M. (?) oolitica, are the only species of this genus recorded 

 for the whole of our British strata. One species, M. decollata, 

 is found in existing seas. 



ZELLANIA, Moore, 1854. 



Etym. — Zella, a lady's name ? 



The generic characters of Zellania, as given by Moore, aro 

 as follows : — " Shell minute, unattached ; foramen large 



